EASTMAN: GAKBONIFEKOUS SHARKS. 93 



Acanthodes and Mesacanthus, namely A. concimius Whiteaves and 

 M. affinis (Whiteaves) from the Upper Devonian of Scaumenac Bay, 

 Canada. 



The occurrence of a new and very large species of Acanthodes in the 

 Coal Measures of Mazon Creek has been previously reported by the 

 writer,-^ but descriptions of the same have been reserved until now. 

 The material upon which the following diagnoses are based belongs to 

 the S. S. Sti'ong colleotiou in the Peabody Museum of Yale College. 

 Nearly all of the vertebrate remains in this handsome collection, com- 

 prising several hundred specimens of the usual concretionary type, were 

 very generously placed in the writer's hands for investigation by the late 

 Professor 0. C. Marsh, and quite recently a number of additional nod- 

 ules have been loaned for the same purpose by Dr. C. E. Beecher. It 

 is hoped that the structure of certain Coelacanths, Platysomids, and 

 Palseoniscids, of which several complete examples exist in the same col- 

 lection, may be elucidated in a future publication. 



Acanthodes marshi, sp. nov. 



Plate 6, Fig. 3 ; Plate 7, Figs. 1, 3. 



To this species are referred a number of large fin-spines, one of them 

 having the dermal rays attached, and also a mass of shagreen granules 

 of correspondingly large size. All these specimens are preserved in 

 ironstone nodules from the well-known Mazon Creek locality in Grundy 

 County, Illinois. The scale-bearing nodule, upon which the species is 

 founded, is shown in Plate 7, Figure 1. The shagreen granules oc- 

 cupy a space of several square centimeters, and present the following 

 characters : 



Scales in the form of quadrate granules averaging about one square milli- 

 meter in size, smooth and polished externally, gently convex or rounded on 

 both the outer and attached surfaces. Internal structure consisting of fine 

 layers of dentine arranged in quadrate fashion about a small central pulp- 

 cavity. Attached surface of some scales crossed by a shallow diagonal groove. 



Not only are the scales much coarser than those of A. hronni and 

 A. wardi, which attain as large a size as any, but the fin-spines are 

 considerably longer and stouter, averaging about 9 cm. long, and from 

 5 to 8 mm. wide. The spines are gently curved backward throughout 

 their length, have tapering distal extremities, and are faintly grooved 



1 Science, n. s., Vol. IX. (1899), p. 642 ; ibid., Vol. XI. (1901), p. 795. 



