INSTITUTE OF SCIENCE, PHILADELPHIA. 73 



as may be proved by the use of a mirror. This may or may not be true 

 as a general thing, but the rule certainly does not hold in the case of the 

 mutually representative species here referred to. The obliquity in F. 

 contrarius is decidedly more pronounced than in F. rapum. 



I am not exactly satisfied as to the relation which this species holds 

 to the recent forms. It certainly most nearly approaches F. pcrversus 

 of Linnaeus, and I must admit that it is undistinguishable from -some of 

 the non-spinose varieties that are usually referred to this species. Whether 

 these last, however, are specifically distinct from the typical spined F. 

 pervcrstts I am not prepared to say; they certainly have much the same 

 general facies, and they would appear to grade into one another. Still, the 

 distinguishing characters rounded body-whorl, absence of spines, and a 

 more closely-enveloping spire in the non-typical form are well-marked, 

 especially in the case of the fossils, where they appear to be constant, and 

 may serve to characterize a good species. But whether distinct or not, 

 it is positive that the fossil is represented in the living fauna. Our collec- 

 tion contains one very ponderous form, which retains all the distinctive 

 characters of the smaller individuals, and may be immediately separated 

 from F. pcm<ersus by its great convexity, the rounded outline of the body- 

 whorl, and its pear-form. 



Dr. Gill (op. cit.) erroneously refers to this species the form described 

 by Tuomey and Holmes, in their work on the Pliocene Fossils of South 

 Carolina, as Busycon pcrversum (pi. 29, fig. 3). The species in question 

 is Conrad's F. adversarius, referred to (Am. Journ. Conch., iii, p. 185) as 

 the " only reversed form with tubercles instead of spines," but which, as 

 far as I am aware, has thus far never been described. 



Fulgur excavatus, Conr. 



Am. Journ. Science, xxxix, p. 387; Foss. Med. Tert. Form., pi. 45, fig. 12. 

 Cassidulus Carolinensis , Tuomey and Holmes, Pliocene Foss. S. Carolina, p. 147, 

 pi. 30, fig. i. 



Common on the banks of the Caloosahatchie, below Fort Thompson. 



The typical forms of this species can be readily distinguished from 

 the recent F. pyrum, Diilw., by its scalariform spine, more depressed, and 

 slender body, and the much deeper sub-sutural canaliculation, which is 

 also carried further towards the apex. The shell, in addition, appears to 

 be considerably thicker. But these characters do not appear to be 

 invariable, and I am far from satisfied that the species ought not to be 

 classed rather with the recent form than as a distinct type. Numerous 

 intermediate stages unmistakably unite it with F. pyrum. As is the case 

 with the last, this species also exhibits a marked variation in the amount 

 of angulation of the body-whorl, sometimes appearing merely rounded, 

 with only a faint trace of carination, at other times very sharply angulated, 

 and with a decidedly concave shoulder. 



