466 PROCEEDINGS OF THE ACADEMY OF [1897. 



his belief that the San Domingo deposit was Oligocene. This opin- 

 ion has recently been re-affirmed by Dall 4 who considers the Bow- 

 den marls of Jamaica and the beds of similar age in Santo Domingo 

 to be upper Oligocene. 



In considering so small a fragment of the fauna as the Scapho- 

 poda constitute, a full discussion of this question is uncalled for ; the 

 more because the Scaphopods afford no conclusive data. 



Key to species of Scaphopoda. 



I. Shell largest at the aperture, tapering to the apex, 



Dentalium. 

 a. With distinct longitudinal sculpture. 



b. Circular sculpture conspicuous ; tube slowly taper- 

 ing. 



c. Somewhat compressed ; sculpture of many 

 longitudinal cords alternating with threads, 

 crossed by close, circular lamellae. 



D. callioglyptum. 

 c'. Circular in section ; sculpture of many lon- 

 gitudinal alternately smaller threads, crossed 

 by regular, blunt, obliquely encircling stria?, 



D. Tryoni. 

 b'. Circular sculptured inconspicuous. 



c. Tube markedly conical, with 6 or more ribs 

 at apex, secondary and numerous tertiary 

 riblets developed in the intervals, D. gabbi. 

 c'. Tube very slowly tapering, with six narrow, 

 distant and sharply defined longitudinal ribs; 

 intervals wide and plain, D. Cossmannianum, 

 c". Square at apex, with 4 ribs, numerous threads 

 soon developing in intervals but lost on larger 

 part of tube, which is circular and smooth, 



D. dissimile and var. ponderosum. 

 a'. No longitudinal sculpture. 



b. Tube nearly or quite circular in section, almost 

 straight, slender, considerably tapering; smooth 

 and polished, D. hay tense, 



b'. Tube ovate in section, being laterally compressed ; 

 slowly tapering, thin, smooth ; apex with a terminal 

 "sheath " and v-shaped slit, D. pyrum. 



*Proc. U. S. Nat. Mus., XIX, p. 304, 1896.' 



