536 PROF. C. H. o'dONOGHUE : REPOKT ON 
Family PLEUEOBEANCHID.^. 
The PleurobrancliidiB have not the large liead-sheath of the BuUidas nor 
the large parapodia of the Tethyidse. They have a well-developed oral veil 
on a head marked off from the body. The oral tentacles are only moderately 
developed and cleft ; the rhinophores are usually considerably larger and 
are deeply cleft longitudinally. The back is covered with a thick or a thin 
mantle and this generallj^ projects freely over the head anteriorly and over 
the tail posteriorly. Within the mantle is a more or less large shell (absent, 
however, in Pleuroiranchcea and Oscaniopsis). A single (in Oscanius double) 
genital aperture lies at the front end of the right side of the body. Above 
or below this, but still anterior to the gill, is a prebranchial opening or papilla 
leading into a sac. The gill is frequently tripinnate, and below it lies the 
urinary aperture. At the hinder end of the strand of tissue attaching the 
gill (the gill mesentery) lies the anus (in PleurohranvJura it is above 
the strand). The foot is moderately large and overhung by the mantle 
("save in Pleurobranchwa, where it passes over into the side and back of the 
body). The sole of the tail-region of the foot often bears a gland. 
Genus Berthella Blainville, Man. de Mai. et Conch. 1825, p. 469. 
Type by mouotypy : B.joorosa Blainville, ibid.=^(^Bulla) plumula 
Montagu, Testacea Brit. i. 1803, p. 214, pi. 15. fig. 9. 
Type, therefore, B. plumula (Mont.). 
Synouymy : Cleanthus Leach, Synop. Moll. Gt. Brit. 1852, p. 28. 
[PLEuaoBRAiSiCHUs (pars) Bergh, Malak. Uiiters. 1898, p. 117. 
The shell is haliotidiform, fairly tough, and .shows lines of growth and also 
longitudinal strise which, while faint, are nevertheless clearly visible. It is 
of a translucent amber-yellow colour. 
The animal is plump and oblong ; the mantle covers the whole bodjr, its 
margin is entire, its front and hinder ends rounded, and it is separated from 
the foot by a deep groove. The gill is bipinnate and of moderate size. The 
two dorsal tentacles or rhinophores are inserted side by side between the 
mantle and the oral veil, and are auriform and deeply cleft. The foot is 
truncated anteriorly and bluntly rounded posteriorly where it projects 
slightly beyond the mantle. The labial armature is composed of two plates, 
each built up of a large number of irregularly arranged close-fitting spine- 
like pieces of chitin. The radula is well developed, without a rachidial 
tooth and the numerous pleural teeth have the form of knife-like blades 
bearing denticles at their distal extremities. 
Species Berthella plumula (Montagu), Test. Brit. i. 1803, p. 214. (PI. 29. 
figs. 29 & 30.) 
Body. The body is an elongated oval and slightly flattened. The mantle 
is well developed and ovej-hangs the body all round, save for a narrow strip at 
the hinder end. The oral A'oil also ]irojects in front of the inautle. 
