1876.] 387 [Hyatt. 



differing in the characteristics of the sutures. The similarity of this 

 species to Braikenridgii is delusive; its true affinities place it nearer 

 to nodosum. The resemblance is due to the retention of the common 

 ancestral Pettos-like form until a late stage of growth, or during the 

 entire life of the individual. 



The various changes taking p'lace by growth and development may 

 be studied in any large collection. The contraction of the whorls in 

 size, and the consequent assumption of rotundity, take place in 

 some specimens very markedly, and make them look very like nodo- 

 sum. This change is so great in some very old specimens that they 

 resemble the adult of Bayleanum, though their own adult stage, or 

 younger periods, have the normal form of the true subcoronatum. 

 In many other specimens, however, though of equal size and appar- 

 ently the same age, there are no perceptible marks of such changes 

 either in the size, form of the whorls, or ornaments. 



Stephanoceras Deslongchampsii. 



Amm. Deslongchampsii D'Orb., Terr. Jurass., pi. 138. 



This is evidently a form of the broad abdomened variety of sub- 

 coronatum with prominent spines, described by Quenstedt as a variety 

 of Humphriesianum, and as a transition to the Amm. subcoronatus of 

 Oppel. A remarkably fine specimen in Quenstedt's collection, from 

 St. Vigor, enabled me to make this comparison. I did not find the 

 original in D'Orbigny's Collection. Quenstedt places it in the 

 Braikenridgii series, to which it appears to be allied by the curvature 

 and general aspect of the ribs, but this resemblance it shares in com- 

 mon with forms of the subcoronatum series, especially plicatissimum. 

 The abdomen becomes considerably elevated, and the sides converg- 

 ent in the adults. 



Stephanoceras plicatissimum. 



Amm. Humph, plicatissimus Quenst., Der Jura, pi. 54, f. 3. 



This variety has so close a resemblance to S. linguiferum in some 

 forms that broken specimens are frequently confounded under the 

 same name. There is a very close resemblance in the sparseness of 

 the lateral ribs, and comparative closeness and fineness of the ab- 

 dominal ribs, the prominent tubercles and the form of the wliorl. 

 The mouth lappets, however, the intermediate forms and the young 

 of Linguiferum show its affinity with Sleph. Sauzei to be unquestion- 

 ble, and separate it widely from this species. Further compari- 

 sons show that the real affinities of plicatissimum lie with the stouter 

 forms of subcoronatum, which have been described as closely approx- 



