114 ELASMIAS. 



The kidney was band-like, very narrow. The radula was not 

 isolated entire. The teeth seem to be all alike, but whether 

 the central tooth was lacking was not determined. The teeth 

 have a very long, fine and curved middle cusp and a little 

 cusp on each side." It is obvious that Semper 's "middle 

 cusp" is really the basal-plate. Probably the fragment was 

 seen from below, being mounted upside down. The radula 

 of E. aperta, examined by W. G. Binney, has "an exceedingly 

 large number of teeth" arranged obliquely in waving rows, 

 the teeth of the same type as those of Achatinella (pi. 31, fig. 

 10). 



Significance of the characteristics of Elasmias. The chief 

 characters of Elasmias are those of early stages of Tornatel- 

 lina and Auriculella. The small number of whorls, globose 

 contour, broadened columella, large lamellae and spiral stria- 

 tion are traits of the end of the embryonic and beginning of 

 the neanic stages in the other genera. So far as we may es- 

 timate the affinities of the genus, it is an arrested type, prob- 

 ably not far removed from the ancestral Tornatellinid stock. 

 When the complete anatomy is compared, this view can be 

 tested. Meantime, the very wide distribution of the species, 

 in an area the least favorable for migration, argues for the 

 great antiquity of the genus. As in many other genera and 

 families actually known to be very old, the species are much 

 alike and not numerous, probably due to the general extinc- 

 tion of phyletic side lines. Lamellovum seems to be a special- 

 ized collateral group of the Elasmias stock which has survived 

 in a single isolated locality. 



At first the uterine shell has a slender, somewhat sinuous 

 but not folded columella, and there is no parietal lamella (pi. 

 31, fig. 2, a shell of 0.6 mm. diameter). Immediately after 

 this stage the parietal lamella arises (pi. 29, fig. 9), and the 

 columella broadens (pi. 29, fig. 8). By the end of the em- 

 bryonic stage (pi. 31, fig. 3, diam. 0.8 mm.) the parietal and 

 columellar lamellae are strongly developed. In some species 

 they diminish in relative size in the later neanic stage, in 

 others, such as fuscum and cernicum, the lamellae continue 

 strong. 



