24 IOWA ACADEMY OF SCIENCES. 



which gives it a decided biangular appearance; the costa;" are crossed by numerous 

 fine, crowded concentric lines; and a few larger somewhat imbricated lines of 

 growth. 



Length 24 mm. ; breadth 21 mm. ; height 20 mm. 



Horizon and locality. Limestones of the Hamilton at Iowa City, Iowa. 



This species somewhat resembles certain forms of C. trigonale of Hall, but the 

 very broad, strongly biangular umbonal slope readily distinguishes it from that 

 species. It also approaches some congeneric forms from the Devonian of Europe, 

 especially certain species from the western part of France, recently described by 

 M. CEblerfi 



1 Etude sur quelques Fossiles Devoniens de I'ouest de la France. 



PRELIMINARY NOTE ON THE SEDENTARY HABITS OF PLATYCERAS.* 



BY CHARLES R. KEYES. 



Platyceras is a generic term which has been proposed for a Paleozoic group of 

 moUusks whose shells are " sub-oval or sub-globose, with a small spire, the 

 whorls of which are sometimes free and sometimes contiguous; the mouth gener- 

 ally campanulated or expanded." These fossil shells had been frequently referred 

 to the genus of modern mollusca known as Capulus. In the case of Platyceras 

 as in many other Paleozoic genera, numerous species have been based, not 

 on any apparent distinctive character, but seemingly simply on their occurrence 

 at different geological horizons; and this has given rise to the establishment of 

 many species which are unquestionably invalid. For specific distinction con- 

 siderable importance has been attached to the configuration of the peristome, but 

 even this feature now appears to have little classiflcatory value in the majority of 

 species of the genus. A careful comparison of a large series of different species 

 of Platyceras reveals the fact that the apertural margin in various specimens of 

 the same species often presents considerable variation: a phenomenon not to be 

 entirely unexpected in a group so closely allied to the modern Capulus. 



Notwithstanding the comparative abundance of Platyceras in some of the 

 Paleozoic strata of both this country and Europe direct paleontological evidence 

 of the sedentary habits of the members of this group is not often met with; yet the 

 instances presented, independent of their bearing upon Platyceras, are of unusual 

 significance as furnishing a solution to certain important morphological problems 

 relative to the Paleozoic crinoids. 



From time to time Paleontologists have mentioned the occurrence of Platyceras 

 attached to crinoids and numerous explanations have been advanced, but it was 

 not until about the year 1873 the correct solution was given. In a large number 

 of instances lately examined the gasteropod covered completely the anal opening 

 of the crinoid, the sinuosities in the lip of the Calyptraean shell corresponding 

 exactly to the irregularities of the surface to which the shell was attached. The 

 conclusion, therefore, is that the intimate association of the two organisms was 

 not the result of accidental pressure but that the molluscan shell was actually 

 attached during life. The inference is, then, that the Platyceras was not truly 

 parasitic in its habits, as has been urged by many writers. 



*This and the three preceeding papers were read at the meeting of September 5. 

 1S8S, but through an oversight were omitted from the Academy's proceedings of that 

 year. 



