A SMALL TRIBE

211

CHAPTER XV

TRIBE V.-STENOPIDEA

THE carapace is produced to a laterally compressed rostrum. The first antennæ have two flagella, the second have a scale. The mandibles have a three-jointed palp. The exopod of the third maxillipeds is small, slender, and almost rudimentary. The first three pairs of trunk-legs are chelate, the third pair being the longest and largest. The branchiæ are filamentous; only the second maxillipeds have a podobranchial plume; the hindmost pleurobranchial plume is the largest. The first pair of pleopods is onebranched and foliaceous; the uropods and telson have no. transverse suture.

Family Stenopida.

This being the only family has the characters of the tribe. It contains two genera long included among the Penæidæ, with which they agree in having the third pair of trunk-legs larger than the two preceding pairs, but separated from that group by the structure of the branchiæ. Of the third genus now transferred to this family, the branchiæ have not been described.

Stenopus, Latreille (in Desmarest), 1825, has a long, flat, obtusely pointed scale on the second antennæ, the third trunk-legs long and slender, the fourth and fifth pairs with the antepenultimate joint subdivided, the telson tapering. The genus ranges from the eastern to the western hemisphere and from the Arctic regions to the tropics. Stenopus hispidus (Olivier) is recorded from the Pacific, from Bermudas, and perhaps from Greenland. Spence Bate's figures of this species are reproduced on a re

duced scale in the adjoining Plate. Stenopus spinosus, Risso, is from the Mediterranean.

Spongicõla, de Haan, 1849, has but one species, Spongicola venusta, with an extensive range in the Pacific. The scale on the second antennæ is broad, not ending in a point, and fringed with long plumose hairs. The third pair of trunk-legs have the hand large and thick and the preceding joint short. In the two following pairs the antepenultimate joint is not subdivided, and the terminal joint is tridentate. The telson is ovate. The species is said to live in the beautiful Euplectella and other similar sponges

Aphareus, Paulson, 1875, has the third trunk-legs long and slender; the fourth and fifth pairs with antepenultimate joint undivided and finger unidentate. The telson is acute. The third maxillipeds resemble antennæ, each of the two slender terminal joints being subdivided into four jointlets. The type species is Aphareus inermis from the Red Sea.

BRANCHING BRANCHIÆ

213

CHAPTER XVI

TRIBE VI.PENÆIDEA

THE branchial structure typically consists of a series of plumes, that are attached by, or very near, their basal extremity to the animal, and from a long central stalk send off on each side a single row of branches that divide and subdivide in a variety of ways according to the genus or even the species. The appendages of the trunk are supplied with nerves from separate ganglionic centres, except the last pair, which is supplied not from its own segment but the preceding. The third pair of trunk-legs are chelate, the two following pairs never are. The ex

truded ova do not appear to be definitely attached to the appendages of the mother prior to hatching as in most other Macrura. The first larval form is supposed to be a Nauplius.

This tribe corresponds with what Spence Bate calls the Dendrobranchiata normalia, in allusion to the ramified, or tree-like structure of the branchiæ. He allots to it two families, the Penæidæ and Sergestidæ.

Family 1.-Penaida.

The carapace at the sides is deeply produced and carried further back than in the median dorsal line; its rostrum is laterally compressed, this part at least being carinated. Of the segments of the pleon the first three are usually not longitudinally carinate, but the three that follow are almost always much so. The sides of the first are produced so as to overlap the hind lateral margin of the carapace and the front lateral margin of the second

6

segment of the pleon. The telson is generally dorsally flattened or grooved. The eye-stalks are usually twojointed. The first antennæ have two multiarticulate flagella, and the first joint of the peduncle flattened to receive the eye-stalk and laterally strengthened on the outer side by a spine-like process, on the inner by an unjointed appendage often fringed with hairs. The second antennæ have a broad, thin, foliaceous scale, and a long flagellum. The mandibular palp' is never more than twojointed. The third maxillipeds are long and pediform. Both the second and third maxillipeds and the three or four following pairs of appendages carry 'mastigobranchia' or epipodal plates. The first three pairs of trunk-legs are chelate and similar, the second longer than the first, and the third than the second. The trunk-legs with occasional exception of the third pair have the antepenultimate joint unusually long in relation to the penultimate (in this respect agreeing with the Stenopidea and Nematocarcinus).

6

This family includes nearly a score of genera, only one of which frequents the shores of Great Britain. In his very detailed discussion of the family Mr. Spence Bate says that in the Penæide the anterior three segments of the pleon are never carinated, but those that are posterior to them are always extremely so.' Yet he subsequently mentions that Penaeus velutinus, Dana, has the pleon carinated from the second somite to the posterior extremity of the sixth, and he gives a similar account of three of his own species, besides mentioning two others in which the carina begins on the third segment. On the other hand in the description of Penæus gracilis, Dana, he says nothing of any carina on the pleon, but states that all the six segments are dorsally smooth. Similar remarks will apply to other genera. In Sicyonia, for example, he describes species which have the carina of the pleon extending from the first to the sixth segment, and in Gennadas species that have no carina on any segment of the pleon except the sixth.

Penaeus, Fabricius, 1798, has a dorsally serrate rostrum,