64 ELOPIFORM FISHES 



are irregular in shape. The thinness of the scale, plus the lack of ornamentation 

 (circuli), imparts a flexibility to this structure. All scales show bone cells in the 

 embedded portion. 



Genus MEGALOPS Lacepede, 1803 



Diagnosis (emended). Megalopid fishes reaching 1 100 mm in length. Neuro- 

 cranial roof markedly convex above the cranial vault. Parietals as broad as long. 

 Dilatator fossa broad, shallow and without a roof. Process of intercalar forming the 

 lateral wall of the periotic bulla. Jugular canal opening posteriorly into the sub- 

 temporal fossa. Maximum depth of the neurocranium occurring at the auto- 

 sphenotic level. Maxilla not extending behind the eye. Scales with more than 

 five anterior (basal) radii. 



Type and only species. Clupea cyprinoid.es Broussonet. 



Megalops cyprinoides (Broussonet) 

 (Text-figs. 30-34) 



Diagnosis (emended). Megalops in which the origin of the pelvic fin lies beneath 

 that of the dorsal. Maximum depth of body equal to or greater than the head length. 

 Dorsal fin with 17-20 rays, anal 24-27 rays. Vertebral column with 67-68 vertebrae 

 of which approximately 30 are caudal. Lateral line with 36-41 scales. Caudal 

 fringing fulcra 1-9 in number. 



Habitat. Coastal fishes, sometimes entering freshwater. Indo-Pacific, between 

 40 N and 40 S. Longitude extremes, east coast of Africa to Society Islands. 



Remarks. Megalops cyprinoides has often been cited in the literature. The 

 following works are considered to be the most important anatomical studies : general 

 cranial anatomy, Ridewood (1904) ; intercalar, with respect to the otophysic con- 

 nection, Greenwood (1970a) ; branchial arches and associated musculature, Holts- 

 voogd (1965) ; ligaments and musculature concerned with the feeding and gill 

 ventilation movements, Vrba (1968) ; otophysic connection, de Beaufort (1909) ; 

 caudal anatomy, Regan (1910) and Hollister (1939). 



The above literature, plus the preceding description of the closely related Tarpon 

 atlanticus, renders an osteological description unnecessary. It remains to point out 

 the various differences between the two Recent forms. 



The proportions of the skull roof above the otic region of the skull differ from those 

 in Tarpon. Thus in Megalops the width at the occiput is relatively greater and the 

 distance from the base of the supraoccipital crest to a line drawn between the auto- 

 sphenotic spines is considerably less than half the length of that line. In Tarpon this 

 latter ratio is considerably greater than half, and thus the length of the otic region 

 in Tarpon is greater. 



The parietals are as broad as they are long and show smooth margins. They are 

 thus like the parietals of young Tarpon but unlike the adult Tarpon condition, where 

 these bones are approximately three times as long as broad and exhibit zig-zag 

 sutures anteriorly and posteriorly. 



