52 Bulletin 4 166 



Gabf s original descriptioji. — Gibbons, nearly equilateral; beaks 

 small, overhanging the area; umbones broad; area narrow and 

 transversly striate; anterior margin narrower and straighter than 

 the posterior, which is regularly curved; surface marked by 

 obscure radiating and concentric lines; hinge rather broad, 

 curved; teeth large. 



''Dimensions. — I^ength .2 in., width .26 in., height of valve 

 .1 in. 



"-Locality. — Hardeman Co., Tenn. Prof. Safford. Also found 

 in the Ripley group of New Jersey." 



We have not had access to Gabb's type of this species and 

 presume it is lost, since Dr. Safford did not send it along with 

 Gabb's other types. However, our collection contains a large 

 number of specimens from a similar horizon and some from ap- 

 proximate localities; hence it seems that since Gabb's figure and 

 description correspond very well to casts of our specimens it is 

 safe to use his term for designating them. 



When studying over and reporting upon the Arkansas material 

 from this horizon it was noted that ' ' The original description of 

 C. inacrodo7ita is more applicable to this form than to those from 

 the typical locality [Matthews' I^anding] inasmuch as the latter 

 possess strong irregular ribbing on the left valve, while in the 

 the right the sculpturing corresponds to Whitfield's description 

 and to that of both valves of the specimens from Arkansas," 

 (1. c, p. 41). 



Not knowing then that Gabb had given a specific name to this 

 form the writer classed it in with C. niacrodoyita which, with the 

 vast amount of material before him at present he regards as in- 

 correct. The name saffordi is here used tentatively in place of 

 older names, transversa or gigantea, for it seems as though it 

 differs somewhat from those species especially in surface marking 

 and in form. The right valve when of ordinary outline and when 

 well preserved looks like the corresponding valve of C. vtacro- 

 donta, and if there were no left valves among a given number of 

 specimens, it would be quite impossible to know to which of the 

 two species, saffordi or macrodonta, to refer them. 



The two valves of saffordi are similarly marked while those of 

 macrodonta vary considerably (see figures). 



There is much variation in the forms of the specimens here re- 

 ferred to saffordi. The most remarkable of which is that figured 

 on pi. 4, fig. I, which is from the so-called Turritella limestone at 

 Hamburg (Josh Hunter's, between Oak Hill and Allenton). 



From the striking similarity of these two species it is quite evi- 

 dent that viacrodo7ita is the direct descendant of saffordi. 



