1921] NATURAL SCIENCES OF PHILADELPHIA. 307 



A very large Stromb, approaching S. gigas in size. 



Strombus ambiguus Sowerby, 



Strombus ambiguus Sowerby, Q. J. Geol. Soc. vi, 1849, p. 48. 



Strongly sculptured spirally, narrower than proximus with less 

 developed spines. There are several strong wrinkles on the col- 

 umellar lip posteriorly. 



Strombus ambiguus form bifrons Sowerby 



Strombus bifrons Sowb., Q. J. Geol. Soc, vi, 1849, p. 48, pi. 9, fig. 9. 



This form or incipient race, becomes somewhat larger than typ- 

 ical ambiguus; the tubercles of the penult whorl are larger and 

 less numerous. It is therefore a more advanced form, in the accele- 

 ration of this sculptural feature forming a transition to S proximus. 

 It has not the posterior wrinkles of the columellar lip of typical S. 

 ambiguus, and the outer lip is smooth or nearly so within. The 

 external spiral sculpture is strongly developed. 



Length 66, diam. 42. mm. 



strombus proximus Sowerby. 



Strombus proximus Sowerby, Q. J. Geol. Soc, vi. 1849, p. 48, pi. 9, fig. 8. 

 Strombus pugilis L., Gabb, Tr. Am. Philos. Soc, xv, 1873, p. 233. 



In this extremely abundant form, the penult whorl bears fewer 



and larger tubercles or spines than in S. a. bifrons. In the prevalent 



form of the race they are larger than on the last whorl. There is 



almost invariably an inferior series of tubercles on the left side or 



very rarely continuing to the hp. Typically the surface is spirally 



striate; but there are transitions to the form having spirals at the 



base only. The lip is either rugose or almost plain within. The 



presence of wide, rounded variceal swellings on the antepenult whorl 



appears to be variable. The maximum length is about 75 mm., but 



55 to 60 mm. is more usual. 



strombus proximus pugiloides Guppy. 



Strombus fragilis Moore, Q. J. Geol. Soc, xix, p. .511. 

 Strombus pugiloides Guppy, Geol. Mag. 1874, p. 433. 



The earliest form of this race appeared in the Santo Domingan for- 

 mation in a form smaller than most proximus. The spines have 

 disappeared from the last whorl or half-wJiorl, and spiral striae are 

 only at the base. The interior of the lip is either smooth or rugose. 

 There are sometimes traces of tubercles of an inferior series. These 

 specimens are transitional between proximus and pugiloides. 



The typical form of pugiloides is that of Bowden. It often shows 

 rufous chevrons on the back, and has invariably a smooth lip. An 



