16 



an antero-posterior direction. This open structure occupies the greater part of the thickness 

 of the centrum . 



The 1904 specimens have this general structure, with a considerable variapce as to the 

 number, size, and disposition of the. openings in the inner tissue. Superiorly there is a central 

 excavation or fossa, with one more or less developed on either side of the centre. Laterally a 

 fossa is present beneath the base of the diapophyses, and on the lower surface there is a 

 median, single, or double fossa. 



Amiurus maconnelli. Cope. 

 Amiurus maconnelli, Cope, 1891. The species from the Oligocene or Lower Miocene beds 



of the Cypress hills. Geol. Survey of Canada, Contr. to Can. Palseont. vol. Ill (quarto), 



pt. I, p. 4, pi. I, figs. 6, 6a-b, la-h. 



The vertebra} of this species differ from those of the preceding principally in having the 

 inner longitudinally disposed tissue more compact. This tissue, in which there is a conspicuous 

 absence of large openings, is made up of slender longitudinal strands with secondary connect- 

 ing ones at right angles to the former, leaving small interspaces. As in A. cancellatus, there 

 are vertical laminte beneath the dense articular surface layer of tissue, but they occupy a 

 greater thickness and consequently restrict the innermost cancellous tissue to a narrower 

 area. 



Cope, in describing the two centra on which this species is based, states that they are 

 without a fossa on the inferior face. This is no doubt an error of observation, as in the larger 

 of the two type specimens there is a single deep fossa below, and in the smaller centrum there 

 is also a single median inferior fossa. 



A few imperfect centra and large vertebral fragments belonging to the collection of 1904 

 are probably referable to this species. 



The lower or proximal ends of a few dorsal fin spines, difiering from those that have been 

 provisionally assigned to Shineastes rhceas, are in the collection of 1904. 



These spines may have belonged to one of the two species of Amiurus here referred to, 

 or possibly both species may be represented. They differ considerably in size, and were 

 apparently without tubercles, or longitudinal sculpture ridges on their sides. From the 

 specimens it is impossible to state whether serrations were present along the anterior, and 

 posterior edges, or not. The sides of the spines were apparently smooth, but the specimens are 

 either slightly worn or weathered so that, any delicate markings, if they were present, have 

 been obliterated. The largest specimen, figures 14, 15 and 16, has a maximum transverse 

 diameter at the base of 13 mm., the smallest does not exceed 4-5 mm., measured similarly. 



The largest spine is one that has been broken off farthest from the proximal end It is 

 subtriangular in section above the base, and is excavated longitudinally behind by a deep 

 groove. Above, the ridge bounding the posterior groove on one side persists, on the other 

 side it disappears, so that the spine is not bilaterally symmetrical. The lateral surface of the 

 spine, on the side on which the posterior ridge continues, is convex, the opposite side is slightly 

 concave. In the centre of the angular anterior surface is a longitudinal, shallow, but well- 

 defined, narrow groove. The basal perforaiion is about 3 mm. wide. Seen sideways the 

 anterior surface curves backward, the posterior outline is almost straight. Measured from 

 back to front, near the distal end of the specimen, the diameter is 12 mm., the transverse 

 measurement at the sarae height from the base is about 7 mm. 



