CA RB ONIFER O US FISH-FA UNA S17 



wide. In Fig. I is shown a very interesting pectoral fin pre- 

 served in counterpart, and retaining the actinotrichia in natural 

 association with the spine. The fibrous rays are quite long and 

 numerous as compared with those of other species, and extend 

 well up toward the point of insertion of the spine. There is no 

 trace here, unfortunately, of a basal cartilage abutting against the 

 proximal end of the spine, nor does this specimen display any 

 of the dermal granules with which the fin-membrane was 

 stiffened, although such are exhibited by a smaller specimen 

 belonging to the Yale Museum. The scales of A. mars hi are in 



Fig. 2. — Acanthodes beecheri Eastm. Coal-measures, Mazon Creek, 111. Resto- 

 ration showing outline of body and position of fins. Xf* 



the form of shagreen granules, averaging about one square milli- 

 meter in size, smooth and polished externally, and gently convex 

 •or rounded on both the outer and attached surfaces. (Fig. la). 

 The internal structure consists of fine layers of dentine arranged 

 in quadrate fashion about a small central pulp-cavity. The 

 best account of the microscopic structure of Acanthodian and 

 Thelodus-like scales is that given by Rohon about nine years 



•ago. 1 



Acanthodes beecheri Eastman. 



Description. — A very small species, attaining an extreme length of about 

 5.5 cm . Body elongated and slender, the maximum depth being contained 

 about nine times 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 

 trunk. Caudal lobe remarkably elongate. Scales extremely minute. 



This species is represented by two nearly complete individ- 

 uals preserved in counterpart and belonging to the Yale Museum, 

 1 Mem. Acad. Imp. Sci. St. Peiersbram, Vol. XLI (1893), No. 5, p. 22. 



