96 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
discussion a survival of the primitive conditions observed in Mesacan- 
thus, with the exception that the free spines between the paired fins 
have become lost. Whereas in most Acanthodians the dorsal exceeds 
the anal more or less in size, in this case it is the anal that is slightly 
the larger. 
The squamation is very fine indeed, and on this account the individual 
granules can scarcely be recognized. The lateral line, however, is very 
distinctly shown in both examples. In the larger specimen the calcified 
meckelian cartilage is preserved on one side, and is substantially of the 
same form as shown by Jaekel’ and Reis? in A. bronni. The smaller 
specimen exhibits a displaced “‘extramandibular spine” with long fine 
rays, such as occurs in A. bronni and A. (Traquairia) pygymea. Teeth 
are absent. By an odd chance a small Pleuracanthus tooth has hap- 
pened to lodge directly over the posterior part of the cranium in the 
larger specimen, thus increasing the obscurity of this region. The com- 
pact structure of the fin-spines and mandibular calcifications leaves no 
room for doubt that these are adult individuals, notwithstanding their 
small size. 
The species is named in honor of Professor Charles E. Beecher as a 
slight tribute of personal esteem, and in grateful appreciation of his 
many friendly courtesies. 
Formation and Locality. Coal Measures ; Mazon Creek, Illinois. 
1 Jaekel, O., Ueber die primaire Zusammensetzung des Kieferbogens und Schul- 
tergiirtels. Verhandl. deutsch. zool. Ges. (1899), p. 252, text-fig. 1.— Zeitschr. 
deutsch. geol. Ges., Verhandl., Vol. LI., 1899, p. 56, text-fig. 1. 
2 Reis, O.. M., loc. cit., Plate VI., Figs. 1, 3, 4. 
