378 Memoirs of the Indian Museum. [Voi,. V, 



without a trace of perfoliations. The cerata are rather thick and some are almost 

 ovate. They are set in four groups. The first, second and third groups are divided 

 into two halves, containing two or three cerata on the right and left respectively. The 

 fourth is a clump of seven cerata disposed irregularly across the back. The vent is on 

 the right side about half way down. The shape of the body is elongate and the tail is 

 moderately long. The foot is expanded into a distinct margin all round the body. In 

 front it is rounded and ample, but not produced into horns or other appendages. 



The cutting edge of the jaws bears a single row of denticles, blunt and shaped 

 rather irregularly. The radula consists of a single row containing 27 yellowish teeth, 

 of which two are still in process of formation. The teeth are of the horse-shoe shape 

 with a moderately strong central cusp. On either side of it there are usually seven 

 denticles. Of these five are long, pointed and conspicuous. The outermost and that 

 nearest to the central cusp are considerably smaller and sometimes hardly visible. 



These specimens cannot be assigned with certainty to any of the tropical species 

 described under the names of Cuthona and Cratena, and most of these must be 

 regarded as merely provisional. In describing small Aeolids of inconspicuous coloura- 

 tion and without any very salient characteristics, it is particularly desirable to 

 examine a large series of specimens and ascertain what variations occur in the size 

 and markings of the body and in the details of the teeth. But unfortunately there 

 is rarely sufficient material for such an examination and it is consequently difficult 

 to say whether the characters considered as specific really have such importance. 



The present species is certainly distinct from C. annandalei described by me in 

 the Records of the Indian Museum (vol. V, 1910, p. 248) but it is remarkable that 

 both were found in brackish water and feeding on similar hydroids (Bimeria). For 

 the name of the genus see my Supplement to Alder and Hancock's Nudibranchs, 

 p. 129. I do not think that the genera Cuthona and Cratena can be maintained as 

 distinct and Cuthona is the older name. 



Elysia chilkensis, sp. nov. 



The notes on the living animal are as follows : — 



" A single specimen taken among weeds in a few inches of water close to the shore 

 at Mahosa in the outer channel of the Chilka Lake, 2o-iii-i9i4. 



Form of body elongate and narrow, pointed behind but not produced. Tentacles 

 very slender, tapering, pointed. 



Colouration : — Dorsal surface dull moss-green marbled with a darker shade and 

 dotted with white. Front of head between tentacles brownish, the brownish 

 shade gradually diappearing behind head on sides of body. A colourless 

 streak along the mid-dorsal line behind the head ; a broad dark brown bar 

 along each side of the head interrupted by a whitish streak containing the ori- 

 fice of the tentacle. 1 Ventral surface greenish. 



Specific gravity of water (corrected to I5°C) 1-0260." 



1 If this implies that the tentacle is retractile it is probably a mistake. 



