342 W. H. HTJDLESTON, ESQ., M.A., F.E.S., ON THE ORIGIN 



strongly bicarinate body whorl, have a singular resemblance to L. sulcata, 

 H. and D. The aperture, however, presents considerable differences, and 

 in this respect Limnotroclms thomjisoni more nearly approaches some of 

 the many varieties of " Littorina " dorsetensis, the chief difference being 

 that in the latter the umbilicus is closed and the aperture is not free as 

 in the former case. Nevertheless, the general resemblance is sufficiently 

 striking. 



b. Chytra {Limnotrochus) JcirHi, Smith, with Onustus ornaiissimus 



nOrhigny. 



See pp. 229 and 350. Originally the empty shell had been described 

 and figured by Mr. Smith {Proc. Zool. Soc, 1881), who classed it under 

 Limnotrochus. Mr. Moore has founded for this species the genus, Chytra, 

 and further observes that the shell of Chytra kirkii is remarkably solid, 

 resembling both that of Solarium and Zenophora {Onustus). 



The resemblance of Chytra to the Jurassic species referred to Onustus 

 is very slight indeed, beyond the general pyramidal shape of the shell. 

 One of the leading characteristics of the Jurassic Onustus is the imbricate 

 overlapping of one whorl over the next one, and this feature is equally 

 seen in the Onustus pyramidatus, Phillips, as in Onustus ornatissimus 

 D'Orbigny. There is no trace of this kind of overlapping in Chytra, 

 which, to my notion, has more the character of Solarium. The basal 

 characters in Chytra are also different to those in the Jurassic species of 

 Onustus. 



Hence I fail to trace any marked resemblance between Chytra and 

 Onustus. Nevertheless Chytra is perhaps the most thoroughly marine in 

 aspect of all the halolimnic series, the shell being thick and more or less 

 free from epidermis. Indeed, most conchologists, if they did not know its 

 habitat, would hardly suspect that it was anything more than a some- 

 what aberrant Solarium. 



6. Paramelania damoni, Smith, ivith Purpurina hellona, UOrhigny. 



See pp. 245 and 345, for figures. There are three species of 

 Paramelania mentioned by Moore (index, p. 366) viz., P. crassigranulata. 

 Smith, P. crassilahris, von Martens, and P. damoni. Other species also 

 have been described by Bourgaignat, some of which possibly belong to 

 Nassopsis. The species of Paramelania selected by Moore for comparison 

 with the Jurassic Purpurina is Paramelania damoni, of which 

 unfortunately I do not possess a specimen, and must therefore rely 

 solely on Moore's figures, pp. 245 and 345. The comparative figures are 

 to be found on p. 345. The particular Purpurina there drawn is 

 P. aspera, Hudl. from the Concavus-htdiS of Bradford-Abbas. This is a 

 very rugose form of Purpurina, and its resemblance to Paramelania 

 damoni (judging from the figure) is very striking ; only that in P. aspera 

 and indeed in Purpurina generally, the anterior notch or channel is more 

 in evidence, and also more reflexed than in the majority of specimens of 



