182 



REPORT ON THE STATE CABINET. 



tinctions might 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 the specimens of A. spiriferoides ^ which is very similar to the A. 

 concentrica of Europe, the disposition of the spiral lamellse 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. 



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

 indicated in the figure at «, from which the two lamellaj proceed for a 

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



y , and recurved upon them- 



' !""■"" ^.-m../' // selves as shown in the 



figure at b, 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 

 con torn' of the shell, being 

 the exterior bands indicated by the dotted lines to c. Farther on, these 

 become expanded and send off" from each one a projecting process at d, 

 and thence are united in a solid plate at e, forming the loop which con- 

 nects the two parts of the spiral arms. It will also be observed that the 

 lamellfe 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 lamellse 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 /«, 

 thus acting as an additional support to the primary lamelljB of the spire 

 in its first volution. The lamellge are represented as cut away at i, 

 showing but a single volution. The remaining portions of the spires 

 consist of simple volutions arranged in a conical form. 



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

 widely distributed form in the Hamilton group ; and the Atliyris vittata^ 

 occurring in the limestone of the Uj)per Helderberg group ; and also in 

 the Hamilton group of Iowa. 



