part 4] THE EVOLUTioisr or liassic gastropods. 339 



indication of the commencement of an anterior canal. This would 

 suggest that it is a member of the Procerithidse ; we originally 

 thought that such was the case, for the general style of ornamenta- 

 tion and the shape of the whorl lead one to suspect that it is 

 near the Froceritliium-ogerieni stock, and arose as a distinct species 

 by the accentuation of the anterior set of tubercles. However, 

 owing to the presence of heterostrophic embrj'-onic whorls and the 

 presumed absence of a canal, we consider it advisable to put this 

 species, provisionally at least, among the Mathildiidae. 



This grouping together of species with heterostrophic embryonic 

 whorls assumes that the latter feature is of great importance 

 in classification. There is considerable variation in the hetero- 

 strophic embryonic whorls in different examples of the same 

 species ; but in such groups we have found no examples with 

 homoeostrophic embryos, and this character appears to be of greater 

 value in classification than we had originally been disposed to 

 admit.i 



Locality and horizon. — The holotype was found in the 

 Lower Lias, on the tunnel-heaps at Old Dalby (Leicestershire). 

 The specimens described here (J. W. Tutcher coll., No. 1002), 

 and other specimens preserved at University College, Nottingham, 

 were found at the same locality. 



Family CCELOSTYLINID^ Cossmann. 



BoTJEaTJETiA Cossmann. 

 BoTJRGUETiA DESHATESEA (Tcrquem). 



TurriteUa desliayesea Terquem (25, pi. xiv, fig. 7). 



T. deshayesea Terquem & Piette (26, p. 37). 



Bourguetia deshayesea Cossmann (2, vol. viii, 1909, p. 71). 



Dimensions of om' specimen. 



Length. Breadth. Length of spire. ^^'7^ Sutural 



'' i} J IT angle. angle. 



56 mm. 35 per cent. 65 per cent. 24,° 106° 



A very large shell, having tumid convex whorls separated by deep 

 sutures, ornamented entirely by numerous transcrescentic strise. 



Development. — The apical whorls are not preserved, and con- 

 sequently the early development is not seen ; the nine whorls 

 present are all similar in shape and ornamentation. The oral 

 margin is not preserved. 



Locality and horizon. — The specimen described is from the 

 Lower Lias (hucJclandi zone) of Kedcar, Yorkshire. (In the Tate 

 Collection, Museum of Practical Geology, Jermyn Street, London, 

 No. 8467.) 



^ The presence or absence of heterostrophic embryonic whorls is used in 

 classifying several groups of recent gastropods. 



