314 



PROCEEDINGS OF THE ACADEMY OF 



[Part II 



Ringicula semistriata? Orb., Gabb, Trans. Amer. Philos. Soc. xv, p. 225. 

 Ringicula dominicana Maury, Bull. Amer. Pal. v, p. 21. 



Minute Ringiculas, from 1.3 to 1.'9 mm. long, are abundant in 

 the Santo Domingo material. In shape and sculpture they show 

 a good deal of diversity — forms like R. semilimata, R. guppyi, and 

 others; there maybe three or four species, as species go in this genus. 

 Without more extended study than we have .time for, exact identi- 

 fications cannot be made. R. hypograpta Brn. & Pils., from the 

 Gatun formation, is another similar, but slightly larger, form. 



NUCLEOBRANCHIATA. 



ATLANTIDAE. 



Atlanta rotundata Gabb. Text-fig. 15. 



Atlanta rotundata Gabb, Trans. Amer. Philos. Soc. xv, 1873, p. 201. 



The shell is rather extensively broken. It consists of 5| whorls 

 the first 4 rather closely wound, with sculpture of four spiral threads 

 on the visible part of the penult whorl. The last whorl shows very 

 minute spiral striation under strong magnification, and there is an 

 inconspicuous groove on each side of the periphery, which shows no 

 trace of a keel. If present it must have been membranous. The 

 diameter, as broken, is 2.5 2nm. 



Fig. 14. Atlanta cordiformis Gabb. Fig. 15. Atlanta rotundata Gabb. 



The rounded whorl, without peripheral keel, is similar to that 

 of Oxy gyrus, but the embryonic shell is that of Atlanta. It may 

 form a subgenus oi Atlanta to be called Atlantidea. Atlanta souleyeti 

 Smith appears to belong to the same group. It differs from rotun- 

 data by the moi'e prominent spire. In the figure of the ventral face 

 (fig. 15, above) the spire is concealed behind the lip. 



Type no. 2891 A. N. S. P. 



