260 NEW YORK STATE MUSEUM 



Honeoyea desmata sp. nov. 



Plate 6, fig. 23 



In describing hereafter the genus Paraptyx we have observed its close 

 structural affinity with Honeoyea, notwithstanding a striking difference in 

 the general external expression of the shells. The genera are alike in the 

 possession of a " crescent " of similar structure and surface characters ; but 

 in Paraptyx the posterior hiatus is very obscure, and the surface of the shell 

 carries only fine, regular and closely set plications. It is with some hesita- 

 tion that the species now under consideration is referred to Honeoyea. 

 It has the suborbicular outline of Paraptyx, the transverse crescent and, if 

 there was a posterior hiatus, it was short and narrow, our material not per- 

 mitting the determination of this point. The surface ornament is however 

 so much like that of Honeoyea that we prefer to leave the species with 

 this genus, recognizing it as an interesting intermediary form between the 

 two genera. 



Shell of medium size, orbicular in outline, transverse on the cardinal 

 margin. The crescentic ridge, which is prominent, makes the only inter- 

 ruption in the regular curvature of the margin. Beak slightly posterior. 

 Valve a little longer than wide. Surface convex, sloping evenly with a 

 slight depression outside of the crescentic ridge. Anterior slope short and 

 abrupt ; hiatus if present very short and narrow. Surface ornament 

 consists of 17 primary ribs, which are rather narrow and widely separated. 

 Though these ribs appear to be somewhat flattened, each was crested by a 

 very fine, erect lamella, which near the lower margin on some of the ribs 

 seems to have become double. The broad and flat interspaces bear four 

 fine, elevated striae, two on the slopes of the primary ribs and the median 

 two much closer together, sometimes apparently coalescing. Near the 

 crescent the numerical regularity of the striation becomes slightly modified. 

 The concave surface of the crescent is obliquely plicated. But a single 

 example of this species has been observed, a left valve, slightly imperfect 

 about the beak. 



