280 



REPORT ON THE STATE CABINET. 



The accompanying figure of the hinge-line of Chonetes scitula, greatly 

 enlarged, will illustrate the relations of the tubular spines. 



The nature of these tubes penetrating the substance of the shell, has 

 been pointed out by Count Von Keyseeling,* and shown in his illustra- 

 tions of Chonetes comoides ; but 



this function has been doubted 

 by Prof De Koninck, who regards 

 their obliquely inward direction 

 as a contrary indication.! In 

 many of our specimens, however, lam able to trace these tubes through the 

 substance of the shell fromthe hinge-margin (their 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 obliqviity 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 Chonetes logani and C. scitula.^ 



The following specie of Chonetes are known in the Upper Helderberg 

 and Hamilton groups of New York : 



Ohonetes acutiradiata, 



0. 



arcuata, 



a 



coronata,X 



a 



dejlecta, 



c. 



hemispherica, 



a 



lepida, 



a 



lineata, 



Ohonetes logani, var. aurora, 



0. 



mucronata. 



G. 



jpusilla, 



O. 



scitula. 



a 



setigera, 



a 



yandellana. 



* Geognostiche Beobachtungen auf ehier Reise in das Petschora-land. By Count Alexander 

 Von Ketserling, 1846. 



■f " These grooves do not appear to me to be produced by the cardinal tubes, as M. De Ketser- 

 LiNG thinks, because in this case they should take an opposite direction : I am led to believe that they 

 depend solely on the successive growth of the shell." Hecherches sur UsAnimaux Fossiles, p. 190. 



X The Chonetes littoni, C. maclurea, C. tuomeyi and C. martini of Norwood and Pratten are 

 regarded as varieties of C. coronata (Conrad). 



