TRANSACTIONS OF WAGNER 

 646 



^ TERTIARY FAUNA OF FLORIDA 



south to Key West, Florida, and southwest to Vera Cruz and the Gulf of 

 Campeachy, Mexico, in shallow water. 



This is not the Atra transversa of Portlock (1843), nor of Rogers (Dec, 

 1839). The latter, a CiicullcBa, has been renamed A. [C.) Rogersiana by Nyst 

 (Tabl. Synopt. Arcacees, p. 63, 1848), and A. (C.) Rogcrsi by Heilprin (Proc. 

 Acad. Nat. Sci. Phila. for 188 1, p. 449). 



This species has the rounded nodulous ribs and discrepantly sculptured 

 valves of A. plicatura, with the more rhombic form and solidity of A. impro- 

 cera, with both of which it is doubtless genetically connected. It is not 

 known below the Upper Pliocene. 



Scapharoa (Scapharoa) halidonata n. s. 

 Plate 33, Figure 24. 



Oligocene of the Bowden beds, Jamaica, and of Curasao ; Henderson, 

 Simpson, etc. 



Shell subequivalve, ovate, oblique, inflated ; beaks rather high, strongly 

 bent forward, almost reaching the anterior fourth of the length ; left valve 

 larger, with about thirty-four clear-cut, elegantly sculptured radial ribs; the 

 anterior dozen ribs are usually dichotomous or deeply sulcate ; the ribs on 

 the middle of the shell are grooved with one or two shallow, sharp, incised 

 lines ; the more posterior ribs are wider and flatter with three or more 

 grooves ; those on the posterior dorsal slope are angular, narrower, and 

 usually have not more than one groove, which is nearly obsolete ; the con- 

 centric sculpture is of evenly spaced, fine, elevated lines arched in the inter- 

 spaces and finely nodulating the anterior ribs ; the sculpture is similar on 

 both valves ; the anterior end of the shell is rounded, the base arcuate, the 

 posterior end oblique above and produced below ; the ends of the hinge-line 

 are angulated ; the cardinal area is moderately wide with about three concen- 

 tric lozenges outlined by the grooving; the hinge-line is straight, the teeth 

 numerous and mostly vertical, the two series not interrupted, the posterior 

 distal teeth tending to become irregular in the adult. Lon. of shell 55, of 

 hinge-line 41, alt. 40, diam. 40 mm. ; large specimens reach a length of 68 mm. 



This shell is usually named A. consobrina Sby. in collections, but when 

 compared with the excellent figure of the St. Domingo species given by 

 Sowerby, it is evident the two cannot be united. Sowerby's species is more 

 elongated, with a much straighter base, the beaks smaller and lower, and the 

 height of the shell proportionately much less than in A. halidonata. 



