1903.] Hay, North America?i Cretaceous Fishes. 35 



sas, VI, 1900, p. 340. — Woodward (A. S.), Cat. Foss. Fishes Brit. 

 Mus. IV, 1901, p. 72. — Hay (O. P.), Bibliog. and Cat. Foss. Vert. 

 N. A. 1902, p. 393. 



The following description is based on the type of the species. 

 The matrix containing this fish has apparently formed a large 

 flattened concretion. Of this there are now in the posses- 

 sion of the American Museum four pieces. The largest block 

 presents the head and the anterior half of the fin. Another 

 has been split from the right side and presents the pectoral 

 fin and some ribs and the imprint of some of the opercular 

 bones. A third block shows the body in the region of the 

 anal fin. This piece does not join accurately the largest 

 block, but Cope did not believe that any considerable part was 

 wanting. The fourth block contains the base of the caudal 

 fin and about 10 vertebras. Between this section and the 

 third there is missing an unknown number of vertebras, 

 probably about 8. From a specimen of A. polymicrodus , 

 studied at the University of Kansas, Dr. A. S. Woodward 

 came to the conclusion that there were altogether about 80 

 vertebras, of which nearly 40 were in front of the pelvic fins. 

 This indicates that at least 10 vertebrae are missing in the 

 abdominal region of our specimen and several others from 

 the caudal region. The number of the type of A. aratus is 

 2403. With regard to the dorsal fin Professor Cope's state- 

 ments are not as positive as the specimen seems to justify. 

 The fin begins just above the hinder border of the operculum. 

 Its first ray is supported by a strong interneural bone (PL 

 II, i. n.). The succeeding interneurals diminish rapidly in 

 size, so that after the sixth they are slender. Cope says that 

 the fin is "continuous as far as the specimen is preserved in 

 this region, viz., to the fifteenth vertebra behind the scapula." 

 But there are 22 vertebrae preserved on the block and behind 

 these are the imprints of 8 more; and there are impressions 

 of interneurals as far as over the 28th vertebra. There is 

 also the base of a dorsal ray over the 21st vertebra, so that 

 the dorsal fin must have extended to this vertebra, at least. 

 On the succeeding block there are interneurals and fin rays 

 {i. n., d.r.). Of the latter several must have had their origin 



