124 ELOPIFORM FISHES 



each lobe without expanded bases. Principal caudal rays preceded by numerous 

 basal fulcra, many of which are unsegmented and lie free in the body musculature. 

 Caudal scutes absent. 



Genus PTEROTHRISSUS Hilgendorf, 1877 



1877 Pterothrissus Hilgendorf : 127. 

 1877 Bathythrissa Giinther : 443. 



Diagnosis. Pterothrissidae in which the interorbital distance is approximately 

 one-quarter of the length of the neurocranium. Parasphenoid teeth extending to 

 mid-orbital level. Maxilla with 6-7 teeth. Coronoid process forwardly directed 

 and situated in the anterior third of the mandible. Branchiostegals six in number. 

 Vertebral column with never less than 100 vertebrae. 



Type-species. Pterothrissus gissu Hilgendorf. 



Remarks. The genus is known by two species, the type-species, occurring off 

 the coasts of Japan, and P. belloci Cadenat from off tropical West Africa. Both 

 species are inhabitants of deeper waters. Poll (1953) records that most specimens 

 of P. belloci have been found at the edge of the continental shelf. Information on 

 P. gissu is imprecise but Okada (i960) states that it is found in ' moderately deep 

 water '. Specimens of P. belloci were not examined but it is obvious from the 

 description given by Poll (1953) that it closely resembles P. gissu. The main 

 differences appear to be in the relatively greater length of the head and eye in P. 

 belloci, and the lateral line scale count (85-90 in P. belloci, 99-112 in P. gissu). 



Previous osteological information on Pterothrissus is scanty. Ridewood (1904) 

 briefly noted some differences between Pterothrissus gissu (termed Bathythrissa 

 dorsalis in that publication) and Albula. Gosline (1961) referred to the caudal 

 structure and snout, and Monod (1968) described and figured the tail of P. belloci. 



Pterothrissus gissu Hilgendorf 



(Text-figs. 60-69) 



1877 Pterothrissus gissu Hilgendorf : 127. 

 1877 Bathythrissa dorsalis Giinther : 443. 



Diagnosis. Pterothrissus reaching 400 mm S.L. Length of head equal to 

 25-26 per cent of the standard length. Maximum depth of the head at the occiput 

 and equal to 50 per cent of the head length. Diameter of orbit 27-30 per cent of 

 head length. Dorsal fin composed of 58-60 rays, anal 11-12 rays, pectoral 15 rays, 

 pelvic 10 rays. 99-112 scales in lateral line. Transverse scale count at dorsal 

 fin origin is 7 above and 8 below the lateral line. 



Material. Four specimens were used in the preparation of the following osteo- 

 logical description. Three were donated by Prof. T. Abe of Tokyo University 

 (221 mm, 236 mm and 220 mm S.L.). The fourth is a larger specimen, B.M.N.H. 

 1903.5. 14.142. 



