CLINTON GKOUP. 



299 



298. 2. CALYMENE BLUMENBACHII, Var.? SENARIA. 



PL. A LXVI. Fig. 6a-e. 



Reference Calymene senaria, Conrad, Ann. Rep. N. Y. Geology, 1841, p. 49. 

 Calymene senaria. Hall, Palaeontology N. York, Vol. i, pag. 238, pi. 54, fig. 3. 



Fragments of this species occur throughout the Clinton group. The specimen fig. 6 a has a 

 greater proportional breadth than either the Niagara or Trenton specimens, but I am unable to 

 find any important differences in other respects. The caudal shield fig. 6 Z» is much larger than 

 any specimens seen in the Niagara group. 



Fragments of Homalonotus delphinocephalus and Phacops limulurus (fig. 7 and 8) likewise 

 occur in the Clinton group as low down as the ferruginous sandstones of Oneida county, which 

 appear to be near the base of the formation. They are extremely rare at this period, but their 

 existence is proved, though the circumstances were more favorable to their complete develop- 

 ment at the period of the Niagara group. The Bumastis likewise (Plate A 66, fig. 9) existed 

 in considerable numbers at the same period. The specimens have evidently been a long time 

 macerated in water, and are always separated at the sutures, the central part of the buckler 

 and the entire caudal shield alone remaining of the individual. These fragments are sometimes 

 packed closely together, lying one within the other, and forming layers of two or three inches 

 in thickness. A fragment of a mass of this kind is shown in fig. 9 e, and in the weathered 

 surface the peculiar porous structure of the crustacean covering is sometimes observable. 



The imperfect specimens of trilobites figured on Plate A 66 give a very good idea of the 

 condition of these fossils in the Clinton group, and form a strong contrast with the remains of 

 the same family in the shale of the Niagara group, where the conditions were not only more 

 favorable for their growth and perfection, but also for their preservation. 



Of the trilobites common to this and the succeeding group, the Calymene appears in the 

 lowest position, and no fragments of the other species have been found associated with it. In 

 the middle and higher parts of the group, however, the Homalonotus, Phacops and Bumastis 

 commence their existence. 



665. 3. ACIDASPIS ( Species undetermined). 



Pl. LXVI. Fig. 2. 



Several fragments of the lateral portions of the buckler have been found, and the single 

 caudal extremity figured. The whole are so imperfect, that it is impossible to determine the 

 specific characters. 



