PTEROPODA. 16 7 



Tentaculites scalariformis. 



PLATE XXXI, FIGS. 3-11. 



Tentaculites sealaris. Hall. Geology of N. Y. Surv. Fourth Geolog. Dist., pp. 172, 173, fig. 2. 1843. 



Not T. sealaris, Schlotheim. Silurian Reseai-ches, p. 643, pi. 19, fig. 16. 



T. scalariformis and T. sicula, Hall. Illustrations of Devonian Fossils : Pteropoda. pi. 26, figs. 3-11. 1876. 



Form elongate-conical, straight, somewhat more cylindrical in approaching the 

 aperture; with the apex, in well-preserved specimens, extremely attenuate, 

 and quite solid for one-fourth to one-third of the entire length of the 

 shell. Annulations prominent, subangular, sometimes rounded on the 

 larger part of the cone ; closely arranged and sharply angular near the 

 apex, gradually increasing their distance, becoming less angular with 

 the increase of the size of the shell, and obtuse and rounded towards the 

 aperture; usually but little variation in character on the outer half of 

 the length, where the spaces between are greater than the annulations. 

 Interspaces and annulations, when well preserved, marked by fine, even, 

 transverse striae, of which nine or ten may be counted in the furrows, 

 and half as many on the summit and sides of the annulations. 



In a few specimens there is much irregularity in the distance and develop- 

 ment of the annulations towards the aperture. The extreme point of the apex 

 is rarely or never preserved in our specimens ; but measuring the annulations 

 at the smaller extremity we find that the distance between them increases 

 according to the following figures : taking the measure of the first nine annula- 

 tions in four specimens, we have the following ratio : (1) 9, 5, 3, 3, 3 ; (2) 9, 

 5, 4, 4, 3 ; (3) 9, 5, 4, 3, 4£ ; (4) 9, 5, 4, 3, 2£, 2, 2. The fossils are imbedded 

 in compact limestone, or spread over the laminated surfaces of the semi- 

 argillaceous layers, and the specimens, with rare exceptions, are compressed 

 and often extremely flattened, except the apical portion, which is solid and 

 preserves its form. The degree of compression influences the form of the cone, 

 as may be seen in the figures. In a few well-preserved specimens, the cylin- 

 drical character of the tube towards the aperture is scarcely noticeable, and 

 the whole appears as an elongated cone. 



