1899 ] NATURAL SCIENCES OF PHILADELPHIA. 369 



observed it appears likely that the spreading membrane and its 

 duct are analogous to the mammalian placenta and umbilical cord. 

 This probability is enhanced by the reduction of the albumen gland 

 to a mere rudiment or vestige, evidently of but slight fuQctional 

 importance, and probably throwing the function of supplying nu- 

 triment to the embryo upon the arteries of the uterus. 



In the viviparous Stylodonta something of the same sort occurs, ^ 

 though I do not know that the albumen gland is obsolete in that 

 genus. 



The jaw and teeth are quite what we would expect, though the 

 absence of a cusp on the narrow, central is a further specialization 

 in line with the general degeneration of that tooth in Achatiuida'. 

 In the radula of a uterine embryo, however, that cusp was found 

 developed (PI, XV, fig. 2), and all of the cusps, as would be 

 expected of teeth which had never been used, are longer and more 

 acute. 



The myology offers some interesting characters. As in JRumina 

 (figured for comparison in PI. XV, fig. 10), the retractor of the 

 pharynx (phi r. ) is short and branches from the left retractor band 

 far forward. Unlike Rumina, it bifurcates. We regard the 

 branch br. of the left retractor baud as probably a mere anomaly. 

 It is one of the lateral pedal retractors. All three retractor bauds 

 are free to the proximal root, where they are very shortly though 

 firmly united. This is unlike Rumina, in which the right retrac- 

 tor and the tail retractor are united for a distance nearly as great 

 as the free length of the latter. The anomalous insertion of the 

 retractor of the penis has already been discussed. 



The lung resembles that of Rumina (figured in PI. XVI, fig. 

 15 for comparison) in the absence of large branches on the pul- 

 monary vein, and the mainly transverse venation, which in Xeobe- 

 liscus, however, is much finer and fainter. 



History of the Generic Name. 



In regard to the name herein used for the genus, some explana- 

 tion may be advisable. In a former paper,^ the senior author pro- 

 posed the name Neobeliscus for the species calcareus Born and cuneus 



^See Viguer's paper, or the synopsis given in Man. Condi. (2), ix, r. 

 150. 



"" Nautilus, X, 46 (1890). 

 24 



