214 A HISTORY OF RECENT CRUSTACEA 
segment of the pleon. The telson is generally dorsally 
flattened or grooved. The eye-stalks are usually two- 
jointed. The first antenne 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 
antennez 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 ‘ mastigobranchiee ’ 
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- 
curcinus). 
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 Peneidz 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 Penceus 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, 
