GEOLOGICAL SUKVEY OF THE TEERITORIES. 339 



hemispherical pit of considerable size. Just in front of it is another of ' 

 cresceutic form. 



A partially complete circle of bone, convex on one side, concave on 

 the other, was found with the remains of two species of Portheus and 

 one of IcJithyodectes. They look like a sclerotic ossification, and as 

 though molded on a globe. They are not segmented as in reptilian 

 sclerotic ossifications, nor do they seem to have been completed circles. 



The femoral bones, or those supporting the ventral fins, are preserved 

 in Ichthyodectes anaides and a Fortheus, best in the former. They are 

 closely united posteriorly, the inner margin gradually approximating to 

 the union, which is accomplished by the application of the subcylindric 

 posterior part of the bones. In Fortheus they are united by a coarse 

 suture. There are no posterior processes, but the anterior are long and 

 slender. Each is divided, the inner portion being rod-like, the exterior 

 plate-like. The outer is probably the shorter ; exteriorly it rises into an 

 obtuse ridge on the lower side, and the plate then expands backward 

 as well as outward, nearly inclosing a large sinus with the base of sup- 

 port of the fin. The fin-supporting surface is subround, with two exte- 

 rior and one interior articular surfaces, and a projection in the middle, 

 which has one or two articular faces of smaller size. The base of the 

 anterior projections is rather broader in Ichthyodectes than in Fortheus. 



Three kinds of spine-Wke rays or supports of the fins have been found 

 in connection with remains of species of this family, and the proper 

 reference to their positions and species is as yet in some degree uncer- 

 tain. First, the elegantly segmented compound rays originally referred 

 to Ftychodus by Agassiz, and described by me under the species Sauro- 

 cephalusthaumas, appear to be referable to the genus Fortheus, and to 

 be supports of the caudal fin.* 



Secondly, spines comj)osed of unsegmented rays closely united, edge 

 to edge, and arranged like the fulcra at the base of the external rays 

 of the caudal fin of recent fishes ; that is, the first very short, those 

 succeeding increasing regularly in length to the last, which forms the 

 apex of the spine. The obliquely truncated extremities of these rods 

 from a continuous sharp edge, which is coated with enamel, and may 

 be straight or interrui)ted with low knobs. The former kind belongs 

 probably to Fortheus, and the latter to Ichthyodectes. it is nearly 

 related in character to the S]3ines of Edestus, the enamel-coated knobs 

 of Ichthyodectes rising into veritable teeth in the Carboniferous genus. 

 These spines are unsymmetrical, and belong either to the pectoral or 

 ventral fins. To which they shoukl be referred, it is not now easy to 

 decide. The living allies of the Saurodontidce do not possess ventral 

 spines, nor do they exist in physostomous fishes. In the Siluroids, the 

 pectoral fins are supported by strong spines, which remotely resemble 

 the present oues in their compound character. 



Thirdly. There are numerous flat, more or less curved, spines or rays 

 of small diameter, compared with the length. One surface is covered 

 with a thin, generally striate-grooved layer of enamel, and one edge is 

 trenchant. One side of this edge is more or less obtusely rugose or 

 thickened. These rays thin out to the extremity, which, in some cases, 

 at least, is not contracted. These rays are composed of appressed 

 halves, are unsymmetrical, with basal hook, and belong, no doubt, to 

 paired fins. If those already described are pectoral, these are venjbral, 

 and vice versa. A series of them found together had much the form of 

 either of these fins, while their enlarged number would identify them 



* See Hayden's Report, loc. cit, p. 423, wliere this view is held. 



