NAPLES FAUNA IN WESTERN NEW YORK, PART 2 22 1 



Beushausen construes as Lunulicardium certain suborbicular shells typi- 

 fied by L. ventricosum Sandberger, which he illustrates as a species 

 having a short lunule and with the byssal opening quite or nearly closed by 

 vertical walls ; with a lineate ligamental area (common to all these shells) 

 behind the beak, and the beaks themselves directed forward, or prosogyre. 

 The author suggests that Munster's species L. excrescens is of this 

 type. The reason for dissociating such a form generically from the type of 

 the genus L. semistriatum is not clear to us, and it does not appear 

 that this construction in any way fortifies the genus. This is rather a con- 

 ception or an idea of Lunulicardium than an effort to follow closely the 

 intentions of the author of the genus evident in the descriptions and figures 

 of L. semistriatum as given above ; for the features of this shell are 

 in most particulars clear and quite in harmony with the great majority of 

 forms which, so far as our experience goes, palpably belong to this group. 



In all the extensive material that has been before us, some hundreds of 

 specimens representing this genus, we have seen no instance in which the 

 beaks are not apparently directed away from the umbolateral deflection or 

 lunule, except in the shells we have herein designated as Pterochaenia. 

 While Miinster, Zittel, Beushausen and Holzapfel have agreed in regarding 

 the opening of the valves as a byssal passage, Barrande and Hall were 

 more cautious in their expressions concerning it, the former designating it 

 alternatively as "lunule" or "pan coupe*." 



The great truncation and hiatus in these shells, their most conspicuous 

 feature, may be construed as serving one of the following functions : 

 (i) a siphonal opening, (2) a ligamental hiatus, (3) a mantle opening for 

 the extrusion of water in swimming, (4) a passage for the byssus. 



The first consideration is excluded, as Beushausen has shown from 

 clearly defined external casts from the limestone of Martenberg the contin- 

 uity of the pallial line in several species (see also our figures of L. m ii 1 1 eri 

 and L. i n f 1 a t u m from those localities). While these specimens indi- 

 cate an integripallial shell, it is worthy of note that L. m ii 1 1 e r i displays, 

 both in Beushausen's and our own specimens, a central juxtaposition 



