1921] NATURAL SCIENCES OF PHILADELPHIA. 359 



Distorsio clathrata (Lamarck). This is the ordinary Antillean 

 species, and has no synonyms except the several misappUcations 

 of names really pertaining to the Eastern species, unless Triton 

 ridens of Reeve belongs here, which we are unable to determine in 

 the absence of information on its sculpture. 



It differs from the Oriental species (reticulata) in the evenly 

 rounded back of the last whorl, sculptured with regularly spaced 

 spirals. It is not keeled at the shoulder and the lirae are not con- 

 tiguous there. The two folds on the parietal wall posteriorly are 

 much more nearly contiguous than in reticulata: the third tooth 

 within the outer lip is prominent, and the columellar sinus is deep 

 and narrow. Kiener's figures of a specimen from Lamarck's col- 

 lection are characteristic. (Icon. Coq. Viv., Triton, pi. 14, fig. 1.) 



So far as we know this species does not occur in the Miocene of 

 Santo Domingo; but in the doubtless somewhat later Bowden 

 Miocene a small, but otherwise practically typical race occurs, 

 which has been figured by Guppy as " Persojia simillima Sowb.',' 

 (Quarterly Jour. Geol. Soc. XXII, 288, pi. 17, f. 13.) 



Distorsia constricta (Broderip), (Triton constrictus Brocl., P. Z. S. 

 1833, p.- 5), is similar to D. reticulata in the angular back, this form 

 is more like D. clathrata in the aperture. At the peripheral angle 

 there are two contiguous spiral cords; below these are about ten spi- 

 rals, and above them only one. The intervals between spiral cords 

 have fine spiral striae. 



The third tooth of the outer lip is enlarged; the two posterioi- 

 folds of the parietal wall are rather near together, as in Distorsio 

 clathrata. 



The recent form belongs to the Panamic fauna. It was doubtless 

 derived from the Antillean tertiary fauna where the stock is now 

 extinct. 



The first recognized member of the series is D. crassidens Con- 

 rad, ^^ of the Vicksburg Oligocene. This is small, and differs from 

 the recent forms by having many unequal spiral threads and 

 striae in the intervals betw^een the spiral cords. Its genetic rela- 

 tion to the later Miocene D. c. simillima and the recent D. con- 



^^Triton crassidens Conr., Journ. Acad. Nat. Sci. Phila. I, 1848, p. 118, pi. 11, 

 fig. 40. 

 Distortrix crassidens Conr., Proc. Acad. Nat. Sci. Phila., vii, 1854, p. 31. 

 Distoriio crassidens Conr., Amer. Journ. Conch. I, 1865, p. 20. 



