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 behind. 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. No. 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 fin-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. 
Fic. 14. 
Acanthodes beecheri, sp. nov. Coal Measures; Mazon Creek, Ill. Restored out- 
line. X 2. 
In size and general configuration this species resembles the Devonian 
Mesacanthi, especially Mesacanthus mitchelli (Egerton) from the Scottish 
Old Red 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 specics under 
