FOSSIL AND RECENT 



ep1-2 



147 



un2 



h3-6 



u2 



pu 5 



Fig. 72. Istieus grandis Agassiz. Caudal skeleton in left lateral view. 

 Camera lucida drawing of B.M.N.H. 20586, fin-rays omitted. 



unexpanded bases of the inner fin-rays and the unsegmented condition of nearly all 

 the basal fulcra. Dissimilarities are also evident : /. grandis shows only two epurals 

 (the caudal skeleton of I. macrocephalus is not known in this respect), the second 

 uroneural is relatively smaller, the first uroneural extends forwards to reach the 

 second preural centrum and there are more basal fulcra. In the specimen figured 

 (Text-fig. 72) hypural four is partially fused to the fifth hypural. 



Istieus macrocephalus Agassiz 

 (Text-fig. 74) 



1833-44 Istieus macrocephalus Agassiz : 5, pt 1, p. 13, pt 2, p. 93, pi. 16. 

 1863 ? Istieus macrocephalus Agassiz ; Marck : 39, pi. 4, fig. 6, pi. 5, fig. 3. 

 1 90 1 Istieus macrocephalus Agassiz ; Woodward : 70. 



1954 1 stieus grandis Agassiz ; Siegfried : n. 



Diagnosis (emended). Istieus reaching 250 mm S.L. Operculum twice as deep 

 as wide. Six branchiostegal rays. Vertebral column with not more than 75 

 vertebrae. Dorsal fin with 41-44 rays. Body slender, with a narrow caudal 

 peduncle. 



