142 NEW YORK STATE MUSEUM 



fig. 12] and a shell of very similar character has been obtained in the fauna 

 under consideration. It is a left valve of considerable size, quite strongly 

 and evenly plicated radially with a prominent anterior (byssal) ridge. 

 While the true generic character of this shell and its ally from the Gaspe 

 sandstone is entirely a matter for future determination, the concurrence of 

 these forms in the formations in question is interesting. 



Leptocoelia flabellites (Conrad) 



Plate 34, figures 17-20 

 See pt i, p. 174 ; pt 2, p. 81 



Extraordinarily abundant, of normal or medium size; that is, not 

 attaining the large dimensions reached by the species in the Grande Greve 

 limestones ; often prevailingly small in places but generally holding the 

 characters of the shell in its cosmopolitan distribution. 



Megalanteris diobolaris nov. 



Plate 34, figures 1-5 



A persistently small lenticular .shell with a subcircular outline slightly 

 extended on the front margin ; in size less than that prevailing in B e a c h i a 

 suessana but similar in outline, though generally more rounded. In 

 Megalanteris ovalis and Beachia suessana Hall the lateral 

 margins are notably introverted ; here, however, the introversion is very 

 slight, confined to the shoulders of the valves and noticeable only on very 

 well preserved specimens, particularly internal casts. In interior structure 

 the species is distinctively a Megalanteris. It has a very prominent club- 

 shaped thickened cardinal process more or less deeply grooved at its summit 

 and in extremely thickened specimens deeply constricted by a groove which 

 sets off the cardinal process from its base. The umbonal region of the 

 dorsal valve is thickened and covered with vascular pits and grooves. 



The muscle scars are prominent in both valves as in M. ovalis but 

 not so sharply defined on their anterior edges. Most noticeable, however, 

 as a differential of the species is the unusual development of the cardinal 

 area of the ventral valve which under ordinary preservation stands out 

 prominently above the dorsal valve and is much more pronounced in size 

 than in any other known species. Average specimens of this species, and 

 they are quite uniform in size, have a length across the shoulders and an 

 axial length of about 25 mm. 



I have felt somewhat constrained to identify this shell with Megal- 

 anteris condoni McChesney [Rensselaeria condoni McChes- 

 ney, Palaeozoic Fossils. 1861. p. 85. Chicago Acad. Sci. Trans. 1867. 

 1:36, pi. 7, fig. 2; Meek & Worthen, Geol. & Palaeontol. 111. 1868. 

 3 : 401, pi. 8, fig. 43, b ; Megalanteris condoni Hall & Clarke, Pale- 



