stanton.] AMALTHEIDJE. . 175 



trigonal node or projection at their outer ends, and again become, as 

 it were, pinched up at their inner extremities, which do not quite reach 

 the umbilical margin. 



"Septa moderately close together; siphonal lobe longer than wide, 

 with three or four short branches on each side, the two terminal of 

 which are largest, more or less nearly parallel, and merely serrated; 

 first lateral sinus broader than the siphonal lobe, more or less deeply 

 divided into two subequal branches with short, irregular branchlets 

 and digitations; first lateral lobe somewhat longer that the siphonal 

 and tripartite, with short, irregular branchlets and digitations occasion- 

 ally in small specimens, with the middle terminal branch proportionally 

 broad and so deeply sinuous at the end as to impart more nearly the 

 appearance of a bipartite arrangement of the whole; second lateral 

 sinus nearly resembling one of the divisions of the first, and in the 

 adult with merely a number of marginal digitations; second lateral 

 lobe little more than one-third as long, and from one-third to one-half 

 as wide as the first, generally tripartite at the end, but sometimes, in 

 large specimens, bipartite on one side of the shell (see Fig. Hi of our 

 PI. 7), the divisions being very short and simple, or serrated; third 

 lateral sinus very small and merely bilobate, or in large specimens 

 digitate along the margins; third lateral lobe hardly half as long as the 

 second, and in small specimens (it has not been seen in the large ones) 

 merely tridentate at the end. 



" Largest specimen seen (with a part of the noD septate portion want- 

 ing), 7 inches in its greatest diameter; convexity, measuring between 

 the costse at the larger broken end of the last turn, 1.60 inches; con- 

 vexity of the same, measuring so as to include the greatly expanded 

 costre, 3.25 inches." 



This species was fully illustrated by Prof. Meek (loc. cit.) and copies 

 of several of his figures showing some of the stages of development 

 are here given. So far as can be determined from the figures and de- 

 scriptions of MantelFs types there is no reason for separating the Amer- 

 ican from the English forms, but those figured under the same name by 

 d'Orbigny are entirely different, and it seems to me that the forms re- 

 ferred to Ammonites woolgari by Schluter 1 probably also belong to 

 another species. Ammonites bravaisianus and A. carolimis are probably 

 immature specimens of P. woolgari) as Prof. Meek suggested. At least 

 they can be exactly duplicated by young individuals of the American 

 species. If these really are distinct from Mantell's species I think that 

 our species is also different, but this can not be decided until the young 

 stages of the English form are more fully known, and all the evidence 

 now available supports the opinion that they are identical. 



There has been some confusion in regard to the generic relationships 

 of this species. Meek 2 made it the type of Prionotropis, which he 



1 Scliliiter, C, Cephalop. d. oberep deutsch, Kreicle, Palseontographica, vol. xxi, Pis. 9 and 12, 



2 Op. cit., p. 453. 



