8o 



Memoirs of the Indian Museum. 



[Vol.. II, 



Conchoderma virgatum (Spengler) (1790). 



C. virgatum, Darwin, Mon. Cirr., Lep., p. 146, pi. iii, fig. 2 (1851) ; Hoek, " Chal- 

 lenger" Rep. Zool., vol. viii, Cirr., p. 55, pi. ii, figs. 13—15 ; Turner, Trans. 

 Roy. Soc. Edinburgh, xli (ii), p. 430, pi. i, fig. 3 (1905) ; Annandale, Illustr. 

 Zool. '' Investigator ," Crust. Ent., pi. v, fi.gs. 2, 3 (1908). 



C. hunteri, Darwin, op. cit., p. 153, pi. iii, fig. 3 ; Stehhing, Willey's Zool. Res., 

 Crust-, part v, p. 676; Borradaile, Gardiner's Zool. Geograph. Laccadive and 

 Maldive Arch., part i, p. 441. 



Capitulum flattened, gradually blending into the peduncle ; summit square or 

 obtusely pointed. Membrane thin. Valves small, thin, sometimes imperfectly calci- 

 fied, very variable in shape and in proportional length and, therefore, situated at 

 variable distances from one another, but always remote and embedded in membrane. 

 (Slightly modified from Darwin.) 



Darwin recognized three species of this genus but acknowledged C. hunteri as dis- 

 tinct from C. virgatum with some doubt. Hoek was prepared to unite these two and to 



recognize only C. auritum, a very distinct species, 

 apart from C. virgatum. In this course I have 

 followed Hoek, after examining a considerable 

 number of specimens externally and dissecting 

 several. The one constant difference between C. 

 virgatum and C. hunteri is that of colour, and even 

 this difference is not absolute. The species C. vir- 

 gatum (s. /.) can be distinguished at once from 

 C. auritum by the absence of the " ears" which 

 form so conspicuous a feature of the capitulum 

 of the latter. The membrane, too, is thinner and 

 the lateral appendages have a different arrange- 

 ment ; for in C. virgatitm there are none of these 

 structures at the base of the second cirrus, while 

 in C. auritum there are two in this position. 

 The main differences which led Darwin to recognize C. hunteri as distinct were 

 ''the almost rectangular manner in which the upper portion of the tergum is bent 

 outwards and along the orifice of the sack, the narrowness of all the valves, and 

 especially the lateral lobes of the scuta, and lastly, the greater curvature of the car- 

 ina, which in some specimens runs up far between the terga." None of these charac- 

 ters are constant in the specimens I have examined. The tergum in some is straight, 

 being broader at its occludent end than at its carinal ; in others it is angularly bent as 

 in Darwin's specimens ; in a few it is absent. Similarly, the carina is almost straight 

 in some specimens, strongly arched in others, sinuate in others. The scuta vary in size, 

 in the degree to which they are calcified, and in the relative lengths of the three 

 branches. The one constant character about them is that they are Y-shaped, never 



Fig. 5. — First cirrus of Conchoderma 

 virgatum var. hunteri, x 16. 



