44 



PISCES 



CLASS I 



Promyliobaiis, Jaekel. A skeleton from the Upper Eocene of Monte Bolca, 

 apparently showing pectoral fins less completely interrupted at side of head 



than in recent Myliobatis, otherwise resembling 

 the latter. P. gazolae, Zigno sp. 



Myliobatis, Cuv. (Pastinaca, Gronow), (Figs. 

 87-90). The dental pavement of the jaws 

 consists of seven antero-posterior rows of hex- 

 angular flattened teeth closely pressed together. 

 The lower dentition is longer and less arched 

 than that of the upper jaw. 

 In young examples all the 

 teeth are similar in form and 

 size, but during growth the f\ 

 median series rapidly in- \, 

 creases in width, and event- 

 ually becomes from three to 

 six times as broad as long, 



Myliobatis 



Fig 



toliapicus 



81 >. 



An. 



Imperfect 

 dentition. Middle'Bocene ; Bracklesham, while the shape of the lateral 

 Sussex. . •11 



series remains unchanged. 

 The strongly developed root of each tooth is marked with 

 parallel grooves on its lower and lateral faces. Numerous 

 species represented by the dentition in the Tertiaries, and 

 caudal spines also known. M. dixoni, Ag. ; M. sir kit us, 

 Buckl. ; M. toliapicus, Ag., from English Eocene. M. 

 pentoni, Sm. Woodw., the largest known species, from 

 Eocene, Mokattam Hills, Cairo. M. magister, Leidy, the 

 largest American species, known by complete dentition 

 from the South Carolina Eocene. 



Rhinoptera, Midler (Zygobates, Ag. ; Mylorhina, Gill). 

 Dentition of both jaws strongly arched antero-posteriorly. 

 Teeth flattened and hexangular, in five to nine antero- 

 posterior rows, and mostly broader than long, but diminish- 

 ing in breadth outwards. Tertiary and Recent. R. daviesi, 

 Sm. Woodw., from London Clay, Sheppey. 



Aetobatus, M. and H. (Goniobatis, Le Hon). Teeth very 

 broad, in a single antero-posterior series. Tertiary and Recent ; 

 distribution. 



Fig. i'O. 



Myliobatis serratus, H. 

 v. Meyer. Caudal tin- 

 spine. Oligocene ; Wein- 

 heim, near Alzey. 



wide 



Order 5. HOLOCBPHALI. Chimaeras. 



Pterygoquadrate arcade completely and immovably fused with the cranium. 

 Mandible provided with a very large dental plate on each side, meeting one or two 

 pairs of denial plates in the upper jaw. Gill clefts covered by a fold of skin, so that 

 there is only one external opening. Vertebral axis not distinctly segmented, and the 

 not o chord surrounded by numerous partially calcified rings of cartilage. Paired fins 

 with hvo or three short basal cartilages ; pelvic fins of male with appended claspers. 



The Holocephali occupy a unique position among the Selachii, on account 

 of (1) the incompletely segmented character of the vertebral axis, in which the 

 number of the cartilaginous rings considerably exceeds that, of the arches and 

 processes; and (2) the fusion of the upper jaw with the skull. Their trunk 



