NIAGARA GROUP. 
103 
34 
Homalonotus delphinocephalus. 
Homalonotus delphinocephalus. (Silurian Researches, pi. 7 bis, f. 1 a, 1 b. Trimerus 
delphinocephalus, Green, Monograph, fig. 1, p. 82.) — Head depressed, ovate, sub-acute, 
or rounded anteriorly ; eyes prominent, rather small. Body composed of 13 ribs, with inter¬ 
costal plates; extremities of the ribs directed forward. Caudal extremity distinct, with 12 
ribs united, forming a solid crust; tail acuminate. The whole surface is papillose, or sca¬ 
brous, and in the least exposed portions, this character is often preserved in great perfection. 
It is among the most common trilobites at Lockport. The specimen figured is two-thirds 
the natural size, and they have been seen of twelve inches in length. The young of this 
species, figured by Green, is often found, and sometimes less than an inch in length. The 
name Homalonotus of Konig has precedence over that of Trimerus, but the specific name of 
Green has been retained by Mr. Murchison. 
This fossil and the Dipleura Dekayi have often been most unaccountably confounded with 
each other, notwithstanding their geological relations are so widely different. Dr. Green has 
quoted Lockport as a locality, w'here he remarks it is not uncommon. Rochester, in the same 
geological position, is also named as a locality. All the other places named as producing the 
Dipleura, are in the higher rocks of the system. The separated heads of these species very 
closely resemble each other, but the nature of the matrix is usually very different; and during 
all the excavations at Lockport, I have seen nothing referable to the Dipleura. 
Localities —Lockport, Rochester, Sweden, Wolcott, and numerous intermediate points. 
