DAU,] NOTES ON SOME UPPER CRETACEOUS VOLUTID.E 5 



shells are only moderately thick, the posterior sinus of the aperture 

 is well marked in the adults, and the columellar plaits are small, 

 slender, not crowded, and three or more in number. The character- 

 istics of Volutoderma, which is the most typical of these volutes, 

 include a posterior sinus for the protrusion of a part of the mantle, 

 which in the enameled species (Volutomorpha) serves to distribute 

 the glaze. 1 Judging by recent species, many of which have a similar 

 sinus, the mantle edge as a whole is not extended over the shell 

 except in the genus Zidona. Those authors who have referred 

 members of this group to the Pleurotomidas have therefore insuffi- 

 cient basis for that opinion. 



Beside the sinus, the small smooth shelly protoconch, the ap- 

 pressed suture, the whorl often excavated above the shoulder, the 

 reticulate sculpture, and the three plaits on the pillar often lagging 

 behind the aperture, are characteristic of most of the species where 

 ever found. In many cases the edge of the outer lip where the spiral 

 ridges terminate is provided with a small denticle corresponding to 

 each ridge, and it is not uncommon to find a ridge of enamel in the 

 wake of the posterior sinus, which forms a sort of fasciole. 



Among the types represented are the piruliform, in which the 

 spire is almost involved within the outer whorls and elevated very 

 little above them, while the whorls are rounded and inflated behind. 

 This has been named Ficulopsis by Stoliczka. Its analogue in the 

 Aachen chalk is Ficnlomorpha Holzapfel ; in the Martinez of Cali- 

 fornia, Retipirula Dall 2 ; in the Eocene of Gatun, Panama, this type 

 has a successor in Glyptostyla Dall. In these forms there are two 

 to five plaits. 



Another type has also a low spire, but with the shoulder keeled 

 or angular, the whorl behind it flatfish and the sides of the whorl 

 in front of the keel flattened as in the genus Conns. This is named 

 by Stoliczka Gosavia, and has representative species in the Gosau 

 and Aachen formations and probably one in New Jersey. Accord- 

 ing to Stoliczka and d'Archiac, there is an Eocene species G. dentata 

 (Sowerby) in the Nummulitic of India, which Noetling also reports 

 from the Miocene of Burma. 



1 This sinus differs in function from that of the Pleurotomidse. In the latter 

 group it allows the protrusion of an elongated tube which carries the fecal 

 matter outside the cavity of the mantle (as in Pleurotomaria) and thus pre- 

 vents fouling the water which has access to .the gills. In the Volutidse the 

 anus is anterior and its products are ejected more or less laterally, as in the 

 majority of Prosobranchs. 



- Turbinclla crassitesta Gabb, Pal. Cal.. n, pi. xxvi, fig. 37, 1869. is the type. 



