TRENTON LIMESTONE. 



185 



241. 2. BELLEROPIION BILOBATUS, var. ACUTUS. 



I'l,. XL. Figs. 1 a, b, & f) a, b. 

 Compare Rellcrophon aciUiis, Sowebdy in Sil. Researches, pag. 61'!, pi. I'J, fig. II. 



Involute, suboibiciilar, compressed, elongated ; last whorl acutely angular ; aperture 

 oblong, .sublriangular ; surAice smooth or finely striated ; umbilicus small. 



The lenglli of tliis .shell is about once and a half ihe height, and the height twice the 

 breadth. It is more elongated and less orbicular than the figure of 7>. acutus of Sowerby ; 

 it is also less acutely cariuated, particularly at the commencement of the involution. The 

 acutely angular, almost carinated, dorsal margin, contrasts strongly with the prevailing 

 forms of B. bilobatus ; and this deviation does not appear entirely the efifect of pressure, 

 but is an original character of the shell, which, in other important particulars, retains the 

 features of the species. 



Fig. 4 a, b. Dorsal and lateral view of the specimen. 



The specimen fig. 5 presents another variety of this species, which is apparently due to 

 pressure. The aperture is broadly expanded, and in form like the characteristic varieties; 

 but the siiell is rapidly compressed below, becoming sharply angular, and even distinctly 

 carinated. The striae are similar to those of the more globose varieties, but meeting m a 

 more acute angle on the dorsal line. 



These varieties all occur in a similar position in the strata, and in Ihe same localities, 

 and are all doubtless referable to the single species. 



242. 3. BELLEROPHON BILOBATUS, var. CORRUGATUS. 



Pl. XL. Figs. a, b. 



This shell has the fornr of the B. bilobatus.) with similar surface markings. The dorsal 

 side, below the aperture, is characterized by strong folds which reach half way to the 

 umbilicus. These folds are more or less developed in different individuals, sometimes 

 becoming as distinct as in the one figured. The aperture in such specimens is more angular, 

 and the sinus on the dorsal margin less regularly curved. In other respects there appears 

 to be no essential difference between this fossil, and that marked by simple strire. Both in 

 the specimens having this character, and in those with stria alone, the dorsal margin is 

 sometimes obtusely angular, and in others llattened. 



The specimen fig. 6 a is in a stone with three others, only one of which shows a slight 

 development of these dorsal folds. 



Fig. 6 6 is a specimen less distinctly corrugated. 



This variety of form occurs in the same localities and position as the preceding ; being, 



however, of comparatively rare occurrence. (Cabinet of Mr. Moore, Trenton Falls.) 



[Palaeontology.] 24 



