NAPLES FAUNA IN WESTERN NEW YORK, PART 2 2 I 7 



to be carefully studied. These representatives of Lunulicardium, Cardiola, 

 Buchiola, Dualina, Panenka and other hingeless shells are numbered by 

 some hundreds of specific names. 



The Cardioconch condition 



It was the opinion of Neumayr that such lamellibranchs as the genera 

 above mentioned, which we have specially to consider in the Intumescens 

 zone fauna, represent a simple and primitive type of molluscan shell struc- 

 ture expressed mainly and generally in the absence of cardinal apophyses. 

 Basing his inference chiefly on the data supplied by the Bohemian Upper 

 Siluric species, he designated these shells Palaeoconchae — a name expres- 

 sive of an idea and not designed to take ordinal value. To Beushausen, 

 having in mind the exuberant development of these shells in late Devonic 

 time and only their sporadic appearance in faunas older than Upper Siluric, 

 the name has seemed inappropriate, and he has proposed to call them 

 preferably Cardioconchae. In this term, eliminating the time element in 

 the designation, there also lurks an element of danger if it conveys the 

 notion that ancestrally or actually these genera are necessarily related to 

 the genus Cardium. The cardioconchs are in our judgment simply an 

 expression of uniformity in or convergence to the obliteration of all hinge 

 structure. We may speak of a cardioconch condition and of species as 

 cardioconchs which have attained this condition, but should not employ 

 the term otherwise than as an expression of a peculiar morphologic equiva- 

 lence. . The primitive aspect of the hinge in this phase or state is supple- 

 mented by other primitive features, notably the tenuity of the shell 

 substance. Such manifestations of denticulation as are at times shown by 

 some of the genera, e. g. Buchiola, are reversions to the condition of the 

 provinculum and are not of the nature of permanent dentition. In the 

 absence of permanent apophyses of articulation, this end is frequently 

 attained by interlocking of the ends of the plications along the dorsal line. 

 (Ontaria, Lunulicardium, etc.) r 



x The minute planktonic shell described by Simroth asPlanktomya henseni 

 has on the hinge such denticulations as are shown by Buchiola and it seems probable that 



