214 A HISTORY OF RECENT CRUSTACEA 



segmpnt of the pleon. The telson is generally dorsally 

 flattened or grooved. The eye-stalks are usually two- 

 jointed. The first antennaa 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 un- 

 jointed appendage often fringed with hairs. The second 

 antennffi have a broad, thin, foliaceous scale, and a long 

 flagellum. The mandibular ' palp ' is never more than two- 

 jointed. The third maxillipeds are long and pediform. 

 Both the second and third maxillipeds and the three or 

 four following pairs of appendages carry ' mastigobranchiae ' 

 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 Nemato- 

 carcinus). 



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 Penaaidae 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 Penceus velutinus, Dana, has the ' pleon cari- 

 nated 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 Pencaus gracilis, Dana, he says nothing 

 of any carina on the pleon, but states that all the six seg- 

 ments 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. 



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



