EASTMAN: CARBONIFEROUS SHARKS. 95 



in the total length. Pectoral spines not much stouter or longer than the 

 others; pelvic fins small, slightly nearer the pectorals than the anal ; anal fin 

 slightly larger than the dorsal, which is placed immediately beliind. Length 

 of dorsal and anal spines greater than maximum depth of the trunk. Caudal 

 lobe remarkably elongate. Scales very minute. 



This species is represented by two nearly complete individuals pre- 

 served in counterpart, one of which has a total length of about 5.5 cm. 

 (Yale Museum Cat. Xo. 630), and the other about 5 cm. (Cat. No. 114). 

 Neither of these exhibits the caudal region in its entirety, however, 

 and the heads are not satisfactorily preserved. Only the dorsal and 

 anal tin-spines, with their dermal rays, are displayed by the larger speci- 

 men ; but in the smaller individual all the fin-spines are preserved, 

 although the dorsal is slightly displaced and the distal ends of the pec- 

 torals are wanting. The accompanying text-figure 14 is of composite 

 nature, being based upon both specimens ; it represents the general out- 

 line and proportions of the fins, the restored parts being shown in dotted 

 lines. 



-^ 



Fig. 14. 



Acanthudes beecheri, sp. nov. Coal Measures ; Mazon Creek, 111. Restored out- 

 line. X f. 



In size and general configuration this species resembles the Devonian 

 Mesacanthi, especially Mesacanthus mitchelli (Egerton) from the Scottish 

 Old Eed Sandstone, and M. affinis (Whiteaves) from the Upper De- 

 vonian of Scaumenac Bay, Canada, but differs from them as well as from 

 other species of Acanthodes in the position and relative proportions of 

 the fins. The most marked characteristic of the present form consists 

 in the small size of the pectorals as compared with the pelvic, dorsal, 

 and anal fins. In this respect it furnishes an exception to the generali- 

 zation that in the course of geological time the pectoral fins of Acantho- 

 dians become enlarged at the expense of the pelvic, while the two pairs 

 become approximated. In the Lower Permian A. bronni the pelvic 

 fins are greatly reduced, and in the so-called Traquairia, from the same 

 formation, they are entirely wanting. We have in the species under 



