ORISKANY FAUNA OF BECRAFT MOUNTAIN 29 



were, hence, not altogether satisfactory for identification. Specimens of 

 this genus in the fauna under consideration are of not inconsiderable 

 size and seem to represent but a single species, characterized : 1 by 

 the sharp, concentric lamellae of the surface ; 2 by the broadly expanded 

 aperture ; 3 by the well defined median ridge on the earlier parts of 

 the shell, on which the striae have a pronounced retral bend, the ridge 

 becoming obsolete at the margin. The specimens have the proportions 

 and curvature of C y r. e x p a n s u s, and two of the figures cited (4a,b) 

 show evidence of the concentric markings and the definition of the 

 median ridge. Squeezes from casts of the exterior show a very fine 

 radial striation between the concentric lines. The ajiertural slope beneath 

 the coil bears a broad median sinus bounded by low, divergent ridges 

 which modify the peristome. 



The species is not uncommon. 



Pleurotomaria sp. 

 A single specimen of this genus has served as the surface of attach- 

 ment for a large colony of Fistulipora, and before this coral 

 began its growth the shell had become more or less covered with 

 Spirorbis and Hederella. Thus, while its form is preserved with- 

 out distortion and the slit-band is clearly shown, the character of its 

 ornament can not be made out, and it is unwise to attempt a definition 

 of the specific characters. 



Diaphorostoma desmatum, sp. nov. 



Plate 3, flg. 13-19 



1892. Diaphorostoma sp. nov., Clarke, op. cit. p. 413 



Prof. Hall embraced within the species Diaph. ventricosum a 

 series of small shells which are associated with the large, normal form 

 of that species, regarding them as young stages. Similar shells are found 

 very abundantly in the Becraft mountain Oriskany, and we find from a 

 careful examination of the best external casts obtainable that there is a 

 difference in the two in respect to superficial characters; for, while in 

 the large and ventricose shells the lineation consists of crowded, con- 

 centric growth lines which become wrinkles on the last whorl and seem 



