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a podobranchia to the second maxillipeds, and there are no traces of pleurobranchiæ although pleurobranchiæ are developed on six pairs of appendages. These are riddles which those who have specimens to compare with the descriptions may be able to solve.

Aristeus, Duvernoy, 1841, is distinguished from Penæus chiefly by the circumstance that on the second and third maxillipeds and the first three trunk-legs it has the podobranchia which the other is without. Aristeus antennatus (Risso) occurs in the Mediterranean and Atlantic, and is described as having a smooth pleon.

Hepōmădus, Spence Bate, 1881, is distinguished from Aristeus by a hepatic tooth on the shoulder of the carapace. Hepomadus glacialis, of which Spence Bate's figures are given in the adjoining Plate on a reduced scale, was taken near Yokohama at the frigid depth of 1,875 fathoms.

Several new genera from Atlantic exploring expeditions have been described in recent years by Professor S. I. Smith, as Hymenopenæus, 1882, meaning the membranaceous Penæus, Amalopenæus, 1882, which, at least in the type species Amalopenæus elegans, has only the sixth segment of the pleon carinate. Some of the lately described genera have names alluding to the great depths from which they were obtained Benthesicimus, Spence Bate, 1881, Benthocetes, S. I. Smith, 1884, Benthonectes, S. I. Smith, 1885, all meaning those that dwell or swim in the abysses of the billowy ocean. Benthesicymus has a submembranous integument, exopods to the limbs as in Penæus, podobranchiæ as in Aristeus, and the last two pairs of trunklegs longer than the preceding pairs. One of the species, Benthesicymus pleocanthus, Spence Bate, was trawled from a depth of 3,050 fathoms in the North Pacific, while other specimens were taken twenty degrees further south in the smaller depths of 450 and 1,050 fathoms. Benthonectes is specially characterised by the multiarticulate flagelliform dactyli, that is the subdivided terminal joints, of the last two pairs of trunk-legs. Xiphopeneus, S. I. Smith, 1885, and Benthocetes have a corresponding peculiarity in the propodi or sixth joint of the same limbs. In some of the

species of the deep-sea genera, such as Benthesicymus and Gennadas, Spence Bate, the eye-stalk sends out a prominently pointed tubercle, with a small circular lens at its extremity, served by a distinct branch of the optic nerve, this single lens being very translucent and without trace of pigment. Gennadas received its name, meaning of a noble race,' because it 'approximates nearer than any other to the little crustacean named Penæus (Kolga) speciosus in Salter and Woodward's map of fossil Crustacea.'

Peteinura, Spence Bate, 1888, meaning 'flying-tail,' is established for a single species Peteinura gubernata (see Plate IX.), founded on a single specimen an inch long, taken at the surface of the Atlantic at night time. There can be no doubt that the supposition is justified that the specimen is an immature form. There is a very long slender rostrum such as is common in larval forms, but the strangest peculiarity is at the other extremity of the animal. The sixth segment of the pleon, which is about as long as the four preceding segments together, carries a pair of uropods of which the inner branch is small and rudimentary, whereas the outer is nearly as large as the rest of the animal, a truly prodigious rudder! If ever the tail could wag the dog, one might expect a parallel to that phenomenon in this instance.

Cerataspis, Gray, 1828, of which Cryptopus, Latreille, 1829, is a synonym, has been lately shown to have almost all the characters of the typical Penæidæ.' Gray referred his Cerataspis monstrosus to the Fam. Nebaliada (Les Schizopodes Latr.),' but Giard and Bonnier say, the antennules, the antennæ are absolutely those of the Penæida; the second maxilla possesses the four characteristic plates; the endopod of the first maxilliped is fivejointed, the second maxilliped is geniculate, the third is transformed into a locomotive appendage; the thoracic legs are provided with long swimming branches (exopods); the first three pairs end in chelæ; the last two are simple, &c.' Referring also to P. J. van Beneden's discovery of the nauplian embryo, they remark that among the Schizopods the nauplian embryo has only as yet been observed

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in the Euphausia, while on the contrary it is very frequent among the Penæida.'

Family 2.-Sergestida.

The branchial system is impoverished or lost, the epipodal plates and podobranchial plumes, when present, being restricted to rudimentary structures on the second maxillipeds. The first pair of trunk-legs, and sometimes the second, are simple, the chelæ of the third are minute, the fourth and fifth pairs are feeble, rudimentary, or absent.

The genera assigned to the family are Sergestes, MilneEdwards, 1830; Acetes, Milne-Edwards, 1830; Petalidium, Sp. Bate, 1881; Sciacaris, Sp. Bate, 1881; and Lucifer, Vaughan Thompson, 1829, a pre-occupied name altered to Leucifer by Milne-Edwards in 1837. A very few remarks must suffice on the discrimination of these genera. In Sergestes the last two pairs of trunk-legs are rudimentary, in Acetes the last but one is reduced and the last is wanting, in Leucifer both pairs are absent. In Sergestes the arthrobranchiæ are wanting, in Petalidium they are found on the second and third maxillipeds and the first three pairs of trunk-legs. In Sergestes, Professor Smith remarks, the branchia are compound phyllobranchiæ, while those of Penaeus in the preceding family are compound trichobranchiæ.

The larval forms of Sergestes have been partitioned into genera and species. The youngest form known is designated Elaphocaris by Dohrn (see Plate IX.); another, and presumably later form, is called Platysăcus by Bate; this is followed by Acanthosōma, Claus, and that by Mastīgõpus of the same author. The species known as adults are very numerous, of very various sizes, from many differing localities, Sergestes atlanticus, Milne-Edwards, being found both in the Mediterranean and in the Atlantic from Greenland to the tropics. The account of the genus occupies eighty-eight quarto pages and seventeen plates of Spence Bate's Report on the Challenger Macrura.'

was the subject of a monograph by Kröyer in 1856, and the interest of the subject seems still very far from being exhausted.

Sciacāris, ‘the shadow shrimp,' is interesting as having a telson which ends in two lateral uniarticulate appendages,' but it is doubtfully founded on three specimens from the Pacific, none of which is adult, and none of which exceeds by more than a hair's breadth a sixth of an inch in length.

Acetes indicus was described by Milne-Edwards in 1830, the type-specimens having been taken at the mouth of the Ganges. According to Spence Bate, these are the only specimens known, so that some one must be responsible for a wrong date when he says that with them in the Paris Museum was a note stating that they were taken in 1852 from a large fish "21 feet in length and 25 broad" (Dicerobates eroogoodoo); its stomach was filled with myriads of these little crustaceans, which were carried away in bucketfuls by the fishermen, and thousands were left scattered about the shore.' As the crustacean is only an inch long, the above-mentioned fish, otherwise known as the Ox-ray, or Sea-devil, which may attain the weight of a ton, and has a mouth large enough to swallow a man, would no doubt find room for a shoal of these little shrimps. The Ox-ray occurs in the Mediterranean, and might well be the 'great fish' referred to in the book of Jonah.

Leucifer is without branchiæ; it has the two anterior pairs of trunk-legs without chelæ, and the chelæ of the third pair imperfect; the ova are carried beneath the trunk, but apparently without any special means of attachment. The genus is widely distributed over the tropical and sub-tropical waters of the Atlantic and Pacific, but is supposed to be limited to the two long known species, Leucifer typus (Vaughan Thompson) and Leucifer Reynaudii, Milne-Edwards. It has been made the subject of an elaborate study by Professor Brooks. After the Nauplius and Zoea stages, the young appear to go through transformations corresponding with those of Sergestes.