NOTICE OF PALEONTOLOGY OF NEW-YORK, VOLUME IV. 153 



be founded; but since all the specimens were essentially solid, it has been 

 a labor of no little difficulty to determine accurately the true character of 

 these internal appendages. By carefully cutting down specimens of A. spiri- 

 feroides, which is very similar to the A. concentrica of Europe, the disposi- 

 tion of the spiral lamellee has been found as shown in the following diagram, 

 which represents only the central portion of the spirals to the end of the 

 first volution. 



Athyris spiriferoides. 



Central portion of the spires. 



The origin of the crura, or point of attachment to the hinge-plate, is 

 indicated in the figure at a, from which the two lamellae proceed for a short 

 distance in a nearly direct line forward, but are soon bent upwards and 

 recurved upon themselves as shown in the figure at ^, whence they are again 

 bent downwards into the cavity of the dorsal valve. From this point the 

 lamellae follow very nearly a direction parallel to the external contour of 

 the shell, being the exterior bands indicated by the dotted lines to c. Far- 

 ther on, these become expanded and send off from each one a projecting 

 process at ^, and thence are united in a solid plate at e, forming the loop 

 which connects the two parts of the spiral arms. It will also be observed 

 that the lamellae are twisted, the exterior part at d becoming the interior 

 at the point of junction of the two parts. This plate, formed by the junc- 

 tion of the lamellae, is sharply bent backwards almost in the plane of the 

 longitudinal axis of the shell ; and thence rising nearly at right angles, 

 becomes bifurcated at /, giving origin to the accessary lamellae g, which 

 are recurved in a plane essentially parallel to the first volution of the spire, 

 and coalesce with it at the points indicated by the dotted lines A, thus 

 acting as an additional support to the primary lamellae of the spire in its 

 first volution. The lamellae are represented as cut away at 2, showing but a 

 single volution. The remaining portions of the spires consist of simple volu- 

 tions arranged in a conical form. 



Under this genus we have the Athyris spirifeitoides, an abundant and 



widely distributed form in the Hamilton group ; and the Athyris vittata, 



occurring in the limestone of the Upper Helderberg group ; and also in the 



Hamilton group of Iowa. 



20 



Published March 1867. 



