244 TWENTIETH REPORT ON THE STATE CABINET. 



opening into the interior being a little within the margin), beginning near 

 the triangular foramen, and penetrating the shell to the upper edge of the 

 area in lines parallel to the sides of the foramen. Those nearest the 

 centre are more closely arranged than those at a greater distance : the 

 former appear on the exterior as minute pustules, sometimes very close to 

 the apex of the shell ; and in receding from the centre, they become more 

 prominent, and attain the character of spines. In some examples, the 

 obliquity of the tubes within the substance of the shell is seen to become 

 less and less on receding from the apex, and they are often curved outwards 

 before reaching the surface ; but the connexion of these tubes with the 

 spines is unmistakable. 



In numerous examples of the casts left by the destruction of the ventral 

 valve, the form of the tubes is well preserved in the infiltrated matter ; 

 and in these casts we often find evidence of the tubes near the centre, 

 where no spines are visible on the exterior surface of the shells of the 

 species, as in Chonet.es logani and C. scitula. 



The following species of Chonetes are known in the Upper Helder- 

 berg and Hamilton groups of New-York : 



Chonetes acutiradiata^ Chonetes lineata, 



" arcuata^\ " logani, var. aurora^ 



** coronata* " mucronata, 



*' deflect a, " "pusillay 



" hemispherical '* scitula, 



** lepida, " setigera, 



C. yandellana. 



The Chonetes scitula, leyida and C setigera occur likewise in the 

 Chemung group, together with a remarkable species, the C. muricatus. 



The Chonetes logani was originally described from the base of the 

 Burlington limestone of Iowa ; and a careful comparison of specimens 

 from that locality, as well as from intermediate points in Ohio, together 

 with casts of the same, has left no doubt of the propriety of referring the 

 Tully limestone species to that one. The criticisms of Prof. Winchell 

 regarding the concentric lamellose lines or ridges, I do not regard as of even 

 varietal value, and the varying conditions in this respect are merely acci- 

 dental. The species is illustrated on Plate xxii of Vol. IV, Palaeontology 

 of New- York ; and every care has been taken to give a true representation 

 of the characters of specimens from Iowa, Ohio and New- York. 



* The Chonetes littoni, C. maclurea, C. tuomeyi and C. martini of Norwood and 

 Pratten are regarded as varieties of C. coronata (Conrad sp.). 



