532 



THE AM ERICA X NATURALIST. [Vol. XXXVII. 



the immediate ancestor of typical F. rapum, and appears to con- 

 nect it with F. maximum or F, fusifortnis. F. rapum differs 

 merely in having faint suggestions of spines on the shoulder, 

 which has again assumed an angular outline ; hut this is not con- 

 tinuous. It represents the first stage in the development of the 

 caricum features. The spines of this species are small and may 

 be compared to the first formed portion of a spine in adult F. 

 caricum, or to abortive spines in the same species. This form is 

 probably the morphic equivalent of Conrad's /•'. maximum var. A, 

 from the Mid-Miocene beds. More accelerated specimens with 

 a similarly contracted form have the spines fully developed in 

 the last whorl, and hence parallel F. tritonis, from which they 

 differ only in the more slender form. This may be called F. 

 rapum var. tritonoides. The terminal member of this branch 

 appears to be the Floridian l-'ulgur coarctum Sowerby, which has 



be of independent origin, since its ancestors are found in the 

 Pliocene strata of the adjoining region. The interior of the 

 shells of this series is strongly lirate, and the shells are generally 



