-244 c 



ported by all of the basilar bones. Six of the latter articulate in the fossa; of 

 the groove of the scapula already described. They are flat, contracted at the 

 middle, and expanded at the extremities. In front of these are two others, 

 of a short, thick, cylindric form, one applied to the superior, the other to the 

 inferior facets of the scapula above mentioned, while the tuberosity rises 

 pedestal-like between them. This structure gives a slight hinge-movement, 

 like the opening of the blades of a knife, and entirely unlike the rotary hinge- 

 movement characteristic of the Silurida;. 



The spine is composed of parallel rods in close apposition. The ante- 

 rior edge being oblique, the extremities of the rods terminate successively at 

 the border, which is trenchant, constituting the offensive part of the spine. 

 The edge is hardened and the adjacent parts of the spine thickened, and in 

 some cases roughened by a deposit of a hard substance resembling enamel. 

 It is either straight, or regularly undulate or serrate, with recurved, acute, 

 tooth-like processes. The smaller species exhibit the serrate character ; the 

 larger, the regular border. In either case, a most formidable weapon is indi- 

 cated, not less admirable than those already described from Paleozoic rocks. 

 There is a considerable resemblance between the serrate type and the spines 

 of the Carboniferous genus Edestus, where the teeth are more developed and 

 denticulate. 



Spines of this type were referred by Professor Agassiz to the cestra- 

 ciont sharks of the genus Ptychodus ; but the structure of the scapular arch, 

 now first described, demonstrates the incorrectness of this association. The 

 increased number of the basilar bones shows clearly that they belong to a 

 peculiar family, which I call the Pelecopteridce. The principal genus receives 

 the name Pelecopterus, leaving the question of its relationship to ErisichtJte 

 an open one. The supposition that these spines belong to Porthens and its 

 allies is, therefore, no longer entertained. 



PELECOPTERUS, Cope. 



The characters of this genus are only known from the bones of the 

 scapular arch and the spine of the pectoral fin. As these have been already 

 described under the head of the family, it remains to discriminate the species. 

 Three of these have come under my observation, which are fishes of large 

 size. They may be readily distinguished by the character of the cutting- 

 edge and the relative size and direction of the component rods. 



