DALL] notes on some upper cretaceous VOLUTID^ II 



Glyptostyla and Miopleiona in having two strong plaits, rather than 

 four or five feeble ones, as in Ficulopsis and its associates, Gosavia 

 and Rostellinda. In each case the presumption is that the species 

 is an offshoot from a local group with more elevated spire and not 

 genetically connected with its exotic analogue. 



In the Oligocene concretions from the Astoria, Oregon, beds below 

 the Miocene, the United States exploring expedition under Wilkes 

 in 1841 collected a specimen of a species belonging to a genus related 

 to Volutoderma which was later described by Conrad under the name 

 of Rostellaria indurata. It was associated with Aturia and other 

 Oligocene' types. The original specimen is an internal cast retaining 

 only small fragments of the shell. With more material, it appears 

 that the species is common to the Oligocene of Washington, and is 

 represented in the Miocene and Pliocene of Oregon and California 

 by a related but distinct species. For these the name Miopleiona is 

 proposed, and it is not absolutely impossible that deep-sea dredgings 

 off the coast may reveal in the future a recent representative. 



The Eocene connecting link between the Cretaceous Volutoderma 

 and the Oligocene representative, on the Pacific coast, is not yet 

 known ; but recent investigation by Dr. Ralph Arnold, of the U. S. 

 Geological Survey, under the writer's direction, have fortunately 

 discovered specimens of Conrad's V. indurata which retain portions 

 of- the outer surface. From these we learn that this species was 

 characterized by slender, elongated form, long strap-like axial ribs, 

 with slightly wider interspaces, which reach nearly to the base of the 

 whorls (in a specimen 70 mm. long), while the whole surface is 

 sculptured by fine, close, threadlike, spiral striations. The plaits are 

 of the type of Volutomorpha and not like those of Volutoderma, and 

 the sutural constriction is obsolete. The genus continues into the 

 Miocene, where it appears in a species in which the presutural con- 

 striction (but not the posterior sinus) has vanished, though the 

 suture is still slightly appressed ; the spire is shorter and blunter and 

 the whole form less attenuated. The axial sculpture is still of slen- 

 der, elongated ribs, but there is no spiral sculpture. The columellar 

 plaits are unchanged. This will take the name of M. oregonensis. 



Having described the origin and distribution of this interesting 

 group of Volutacea, we may close the discussion with a tabular ex- 

 hibit of the groups arranged to show the recurrence of specialized 

 types of form in successive horizons, and with descriptions of the 

 new Cretaceous species previously alluded to. 



In the following table, after the Cretaceous, no attempt has been 

 made to include groups not represented in America (unless Athlcta 



