252 bulletin: museum of comparative zoology. 



finities affect the classification may be more clearly seen in the following 

 synopsis : 



Pectoral fins continuous at the sides of the head; 

 a serrated spine behind the dorsal fin ; 



nasal valves confluent, broadly free behind the isthmus ; 



teeth of each jaw in a broad median and in narrow lateral series Myliobatis. 

 Pectorals not continuous, the two cephalic parts forming one lobe ; 

 no serrated spine behind the dorsal fin ; 



nasal valves in a quadrangular flap, free behind the isthmus ; 



teeth of each jaw in a broad median and in narrow lateral series Aetomylaeus. 

 A serrated spine behind the dorsal ; 



nasal valves in two pointed lobes, not free behind the isthmus ; 



teeth of each jaw in a broad single row Aetobatus. 



Pectorals not continuous, cephalic portions in two lobes ; 

 a serrated spine behind the dorsal fin ; 



nasal valves confluent, broadly free behind the isthmus; 



teeth of each jaw in seven or more rows, median more often 

 broader Rhinoptera. 



Aetomylaeus, gen. nov. 



The body and fins of this genus are like those of Myliobatis and of Aetobatus. 

 It is distinguished from both by absence of a serrated dorsal spine on the tail, 

 from the first by absence of pectoral rays connecting the cephalic with the main 

 lateral portions of the fin, and from the second by the dental laminae, each of 

 which consists of a broad median series at each side of which there are three 

 narrow rows, as in Myliobatis. The mesopterygia are fused with the shoulder 

 girdle, as in Aetobatus. 



This genus partakes of the characters of both the genera mentioned ; but by the 

 grouping of those possessed in common, and by the possession of others peculiar 

 to itself, it appears to he entitled to recognition as distinct from either. The type 

 species is that figured by Gray, 1834, in the Illustrations of Indian Zoology, 2, 

 Plate 101, under the name Myliobatis macula tus, and described by Miiller and 

 Henle in 1841. The species described by Miiller and Henle as Myliobatis milvus 

 has the same structure, and iu all probability Rata nichofii of Bloch and Schnei- 

 der, and Myliobatis vespertilio of Bleeker agree with maculatus in their anat- 

 omy and should be included. Provisionally the genus may be constituted as 

 below. 



No caudal spine ; tail long, slender, whip like ; 



origin of dorsal fin behind the ends of the bases of the ventrals ; 

 back armed with small tubercular spines in the middle ; 

 disk less than twice as wide as long ; 



brown-edged ocelli on the hinder part of the disk maculatus. 



