205 



NOTE ON 

 THE ANATOMY OF THERSITES {HADRA) BIPARTITA (Fer.). 



By S. Pace, F.Z.S., etc. 



Read Sth March, 1901. 



Since the radula appears to be the only portion of the internal 

 anatomy of this well-known form which has as yet been described, 1 

 the following meagre account of the details of its genitalia may not 

 be without interest. The material at my disposal was not very 

 satisfactory. Although I have collected in the district around Cape 

 York, Northern Queensland, where this species is very common, I was 

 not enabled to dissect fresh examples, and the ' colonial ' spirit in 

 which some were pickled for subsequent examination failed to preserve 

 the tissues sufficiently. It has in consequence only been possible to 

 make out with certainty (in two specimens) the few features indicated 

 in the accompanying figures : nothing, however, was noticed with 

 regard to the other organs which appeared in any way to call for 

 especial comment. 



Two absolutely distinct varieties of T. bipartita occur in the Cape 

 York district, and, as far as my observations extend, these varieties 

 never overlap in their distribution. Thus, while in the scrub around 

 Mr. Jardine's house at Somerset a large unicolourous pale variety is 

 the only one met with, at Vallack Point, only a mile or so further 

 south, all specimens are typically bipartite in colouration, though 

 of an equally large size. "Whether there are any differences in the 

 internal anatomy of these two varieties could not be determined : the 

 figures are drawn from a specimen of the unicolourous form. This 

 variety is presumably that referred to by Pilsbry 2 as var. ttnicolor, 

 Cox. The shell is perfectly white, but is covered by a yellowish 

 periostracum, which is usually rather darker over the base of the shell. 

 The shape is vai'iable in this, as in the bipartite form. The extreme 

 examples in my series have the following dimensions : maximum 

 height 5'9 cm., maximum breadth 6*3 cm., and height 4*5 cm., 

 breadth 5-8 cm. respectively. 



The accompanying figure (Fig. I) shows the genitalia in veiy 

 nearly their natural relationships as viewed from behind, the parts 

 being slightly opened out but otherwise not displaced. Two or three 

 convolutions of the hermaphrodite duct (h.d.), as well as the terminal 

 portion of the spermatheca (s.), are missing from the dissection. 



1 Semper: Reisen im Archipel. Philipp., vol. iii, pi. xviii, fig. 16. 



2 Tryon's Man. Conch., ser. n, vol. ix, p. 132. 



