179 Dominican Fossils — Maury 15 



Cylichna bidentata Guppy, Quart. Jour. Geol. Soc. London, vol. 32, p. 



518, 1876. 

 Cylichnella bidentata Dall (in part), Bull. Mus. Comp. Zool. Harvard 



Coll., vol. 18, p. 46, 1S89. 

 Tornatina {Cylichnella') ovum-lacerti Dall (in part), Proc. U. S. Nat. 



Mus., vol. 18, no. 1035, 1895. 

 Not Bulla bidentata d'Orbigny, De la Sagra, Hist. Pol. y Nat. Isla de 



Cuba, p. 125, Atlas, pi. 4, figs. 13-16, 1845. Not Cylichna biden- 

 tata Adams, 1850. 

 Not Cylichnella bidentata Gabb, Proc. Acad. Nat. Sci. Phila. , vol. 24, 



p. 273, pi. 10, fig. 2, 1872. (Recent Cuban shell, figured after 



d'Orbigny's. ) 



We collected several hundred shells of a Cylichnella , in the 

 blue clays of Santo Domingo, of which the larger measure 3 mm. in 

 length and 1.25 to 1.50 mm. in greatest width. The majority 

 of the shells are slightly smaller than 3 mm. All are grooved 

 with incised spiral lines only at the base. 



Thus in size and sculpture our fossils resemble d'Orbigny's 

 recent shell, C. bidentata living from Hatteras to Santo Domingo. 

 But the anterior plication in the recent shell is represented in 

 both d'Orbigny's and Gabb's figures as very prominent. In our 

 fossil shells it is so inconspicuous as to be scarcely observable. 

 The posterior fold on the contrary in the fossils is very strongly 

 developed. This appears to be just the reverse of the conditions 

 in C. bidentata. 



In the columellar characters our fossils are more like Guppy 's 

 C. ovum-lacerti, which has a single strong tortuous columellar 

 fold. But our species is much smaller than Guppy 's Trinidad 

 shell and is striate only at the base instead of over the entire 

 surface. Guppy himself pronounced Heneken's Santo Domingo 

 specimens an allied but smaller species. 



Gabb also collected specimens of our species in Santo Do- 

 mingo, as we have some he sent to Cornell (C. U. Museum No. 

 7638), but among them is one single larger shell measuring 4X2 

 mm. This may be that which Dr. Dall unites with Guppy 's 

 ovum-lacerti. None of ours attain that size. 



