On Pterochilus, and two new species of Doris. 329 



thougli rarely, obovate, very tender and delicate, easily torn, and 

 sometimes perforated with a few roundish apertures, undulated, 

 but not crisped. Frustules single or binate, scattered in the ge- 

 latinous substance of the frond without order, oblong, variable 

 in breadth, with the extremities rounded ; when fresh marked, ac- 

 cording to Dr. Dickie, at the four angles with a round colourless 

 spot. When dry the colouring matter contracts on either side 

 and the pale spots are not visible. There is no trace of any stria). 

 The lateral view is very narrow, simply oblong, with the ends 

 rounded. The colour of the plant when chy is a pale green. The 

 frustules do not appear to be decidedly siliceous, but they have 

 the prismatic form of really siliceous frustules. It appears to be 

 quite a spring species. Every specimen had vanished by the end 

 of the month. 



Plate IX. fig. 1. a, Dickiem iihoidcs, iiat. sizo, in different stages of 

 growth ; b, frustules sketched when fresli by Dr. Dickie, liiglily niagiHiied ; 

 c, a frustule observed when dry ; t/, hiteral view of the same ; e, a portion of 

 the frond, less highly magnified, showing the simple and binate fnistnles. 



XLII. — Descriptions o/Pterochilus, a new genus of Nudibrunchiatc 

 MoUnsca, and two new species of Doris. By Joshua Alder 

 and Albany Hancock, Esqrs. 



Gen. Pterochilus. 

 Body oblong, nearly linear, tapering behind. Head anterior, ter- 

 minal, having a flat expanded lobe on each side, forming a kind 

 of veil above the month. Jaws corneous. Tentacvla two, linear, 

 dorsal, vnih. the eyes behind them. Branchia papillary, elon- 

 gated, arranged down the sides of the back. Anus on the right 

 side behind the generative organs. 



This genns is allied to Eolis and Calliopoia, but differs from 

 both in having the head strongly lobed at the sides. It may also 

 be distinguished from the former by having only two tentacula, 

 and from the latter by the gastric system, which in Calliojjaa has 

 two longitudinal vessels down the back, while in Pterochilus there 

 is only one, which is central and undulating. The jaws are tri- 

 angular horny plates, capped at the anterior angles as in Procto- 

 notus. The tongue is narrow, strap-shaped and denticulated. The 

 auditory capsule has a single otolite. 



P. pulcher. — Bodij nearly linear, pale flesh-coloui-ed, spotted 

 with opake white. Head furnished with a flat, rounded lobe on 

 each side of the mouth, forming a kind of veil. Tentacida short, 

 cylindi-ical, set much apart on the head. Eyes considerably be- 

 hmd them. Branchice five or six on each side of the back, in a 

 single series, the first two nearly opposite each other ; the rest 



Ann. li^ Mag. N, Hist. Vol.xiv. Z 



