184 

 Key to the Indian species of Halosaurus. 



I. Ventral fins not united together : — 



1. Head naked, except for a few scales on the temples and upper part 

 of the cheeks : — 



i. Scales on the temples only : nearly half the snout is pre-oral H. anguilliformis. 

 ii. Scales on the temples and cheeks : not quite a third of the 



snout is pre-oral ... ... ... ... E. mediorostris. 



2. Head and snout scaly : half the snout is pie-oral ... ... H. parvipinnis. 



II. Ventral fins united together by membrane [Halosaurichthys] : — 



1. Head naked, except for a few scales on the temples and cheeks ; 



about a third of the snout is pre-oral ... ... ... H. nigerrimus. 



2. Head scaly : not quite two-fifths of the suout is pre-oral ... H. carinicauda. 



146. Halosaurus anguilliformis, Alcock. 



Halosaurus anguilliformis, Alcock, Ann. Mag. Nat. Hist. Dec, 1889, p. 453. 



Halosaurus Hoskynii, Alcock, Ann. Mag. Nat. Hist., Oct. 1890, p. 309: Illustrations op the Zoology of the 

 Investigator, Fishes, pl. VII. fig. 3. 



B. 10. D. 11-12. A. circ. 175. P. 13. V. 1/8. L. tr. 13-14, between D. and V. 



Head naked except for a few scales on the temples, its length about - of the 

 total, and exceeding the distance between the gill-opening and the base of the 

 ventral fin by about an eye-length. 



Length of the snout 2- to 2- in that of the head, the pre-oral portion being 



not quite a half of the whole. 



The major diameter of the eye nearly equals the width of the interorbital 

 space, and is contained six and a half times in the head-length and just over 3 

 times in the length of the postorbital portion of the head. 



The maxilla does not quite reach the vertical through the anterior margin 

 of the orbit. 



The pterygoid band of teeth is very broad and is separated from the pala- 

 tine band by a considerable interval. 



Eight moderately long gill-rakers on the middle of the first arch, besides 

 some small ones above and below. 



Scales extremely deciduous, those on the lateral line larger and more adher- 

 ent than the rest, measuring - of an inch in diameter and having a small central 

 perforation. The scales of the lateral line are thirty in number between the gill- 

 opening and the vent, beyond which they are in contact with the rays of the 

 anal fin. 



The pectorals are slightly larger than the post-rostral portion of the head. 



The dorsal fin begins about an eye-length behind the insertion of the first 

 (outermost) ventral ray. 



