162 Prof. E. D. Cope on the Systematic Relations of Fishes. 



I propose, therefore, to call it the Actinopteri. The character 

 of the five subclasses will then be as follows : — 



Class Pisces. 



The hyomandibular bone continuous with the cartilaginous 

 cranium, with a rudimental opercular bone. Two distinct 

 pelvic bones on each side. Derivative radii sessile on the sides 

 of the basal bones of the limbs, separated from the articulation. 

 Holocephali. 



Hyomandibular bone articulated with the cranium ; no oper- 

 cular or pelvic bones. Derivative radii sessile on the sides of 

 the basal bones of the limbs, rarely entering articulation. 

 Selachii. 



Hyomandibular bone articulated, with rudimental opercular 

 bones ; a median pelvic element. Limbs consisting of the 

 axial line only, commencing with the metapterygium, and with 

 multiplied segments. Dipnoi. 



Hyomandibular articulated, opercular bones well developed, 

 a single cerato-hyal ; no pelvic elements. Limbs having the 

 derivative radii of the primary series on the extremity of the 

 basal pieces, which are in the pectoral fin metapterygium, me- 

 sopterygium, and propterygium. Grossojpterygia. 



Opercular bones well developed on separate and complex 

 suspensorium ; a double ceratohyal, no pelvic elements. Pri- 

 mary radii of fore limb parallel with basilar elements, both en- 

 tering the articulation with scapular arch. Basilar elements 

 reduced to metapterygium and very rarely mesopterygium. 

 Primary radii of posterior limbs generally reduced to one ru- 

 diment. Aotinopteri. 



III. On the Actinopteei. 



In determining the primary types of this subclass, we re- 

 turn to some characters already mentioned, in which they ap- 

 proximate to the Crossopterygia, and, adding others, follow 

 the various divergences to their specialized terminations. 



Thus in Acipenser and allies the ventral fins possess a 

 complete series of basal radial bones, and the pectorals each a 

 large mesopterygium. In Amia and Lepidostens the meso- 

 pterygium is small, and the basal radii of the ventrals are re- 

 duced to their lowest number. In none of them are the basi- 

 hyals fully developed. Most of the Eels retain a character 

 which we have only observed heretofore in the Selachii. 



We pass by a number of the lower fishes before we find the 

 mandibular arch furnished with a symplectic. One of the 

 most important modifications, which is more or less coincident 



