64 
Memoirs of the Indian Museum. 
[VOL. il, 
altogether absent but never showing any tendency to split up in 
a secondary manner. When they are absent or degenerate the 
membrane of the capitulum is greatly thickened ; a muscular layer is 
sometimes present under the membrane. Lateral appendages normally 
present, only absent in a very few instances; anal appendages absent or 
consisting of a single claw-like joint, or multiarticulate. Mandibular 
teeth usually pectinate. Prosoma well developed. Genera — Lepas, 
Conchoderma, Heteralepas. 
Subfamily (c). — P gêcilasmatinæ;. 
Species in which the five valves, unless they are degenerate, cover the 
whole of the capitulum. If degenerate they tend to split up in a 
secondary manner, the scutum being split into two by a vertical break 
in most species. The valves may be almost entirely' absent, but the 
capitular membrane is not much thickened and is not lined by a 
muscular layer. Lateral appendages absent ; anal appendages with 
several joints. Mandibular teeth not regularly pectinate. Genera — 
Pœcilasma, Dichelaspis , Megalasma. 
Subfamily (d). — Alepadinæ. 
Degenerate pelagic forms with transparent membrane devoid of a mus- 
cular layer and with short, straight cirri. Valves absent or represented 
by the scutum only. Filamentous lateral appendages absent ; anal 
appendages absent or consisting of a single joint. Mouth parts much 
simplified. Genera — Alepas (s. s.), Chcetolepas, Microlepas , Anelasma, 
(?) Koleolepas. 
All the genera included in this table are described in Gruvel’s “ Monographie ” 
except (i) Heteralepas , which has recently been established by Pilsbry (1907) for the 
reception of most of the forms previously referred to Alepas and of several new 
species, and (2) Microlepas , which has recently been discovered by Hoek (1907) in the 
“ Siboga ” collection. 
PART I —FAMILY LEPADIDÆ [sensu stricto), 
INTRODUCTION. 
There are few groups in which the subdivision into genera and species is more 
difficult than it is in the Pedunculata, and perhaps this is the case more particularly 
as regards the Lepadidæ than as regards the more primitive forms included in the 
Pollicipedidæ. I have already dwelt on the part played by convergence in the history 
of the group as a whole, and it is perhaps in the Lepadidæ that this phenomenon is 
most manifest. Convergence, moreover, is here accompanied definitely by a marked 
tendency to variation, which is strongest in those forms most degenerate as regards 
their external characters (see plate vi). The early ancestor of the Cirripedes must 
have been a free-swimming crustacean devoid of regular calcareous plates, which 
developed on the integument of its descendants after they adopted a sedentary life. 
