tSENTON LIMESTONE. 201 



263. 16. ORTHOCERAS CLATHRATUM (w. .9^.). 



Pl. XLIII. Figs. 4 a, b, c. 

 Compare Orthoceratites undulatus, Hisinger, Leth. Suecica, 1S37, pag 28, pl. 10, fig. 2. 



Cylindrical, gradually tapering, marked by moderately elevated subangular annulations, 

 longitudinally marked by sharp elevated lines distant jV of ^^ ii^ch in the specimen figured; 

 between and crossing these longitudinal lines are still finer transverse lines or striae, one 

 third the distance of the longitudinal ones ; section circular ; siphunclel 



I have seen but the small fragment of the fossil here figured, but it is quite distinct from 

 any other species in its surface markings. The ti-ansverse ridges are angular, and distant 

 about one half the diameter ; the longitudinal lines are at equal distances, sharp and 

 prominent ; the transverse striae are stronger and more clearly marked than in the preceding 

 species, and distinctly cross the longitudinal ones, producing finely crenulated edges. 



Fig. 4 a. The fragment, natural size. b. Magnified portion of the surface, c. Transverse section. 



Position and locality. In the lower shaly limestone at Middleville. 



264, 17. ORTHOCERAS VERTEBRALE ( n. sp.). 



Pb. XLIII. Figs. 5 a, b, c. 



Cylindrical, very gradually tapering, annulated with abruptly elevated angular ridges, 

 which are distant from each other about one fourth the diameter of the tube, slightly arched 

 upon the back, and direct on the ventral side ; surface marked by strong longitudinal striae 

 and finer transverse ones, giving it a cancellated appearance ; siphuncle apparently central 

 or subcentral. 



The specimen figured is somewhat compressed, scarcely diminishing towards the apex. 

 The septa are not visible, though there is some evidence of a siphuncle at one extremity. 



This species differs from any of the preceding ones, in the abruptly elevated and angular 

 annulations, which are comparatively more distant from each other, and but slightly 

 arched upon the back. The tube is more gradually contracted towards the apex, and the 

 annulations less arched upon the back. In this respect it resembles a species in the higher 

 strata, but is otherwise very distinct from it. 



Fig. 5 a. Ventral side of the fragment. 



Fig. 5 b. Portion of the dorsal side, showing the slightly arched annulations. 



Fig. 5 c. Transverse section of the specimen. 



Position and locality. In the compact limestone at Middlevillej {From Mr. Wadleioh.) 

 [Paljsontology.] 26 



