752 MR. c. TATE REGAN ON [June 19, 



Suborder 2. HYPOTREMATA. 



In addition to the features enumerated above which distinguish 

 the members of this suborder from the Pleurotremata, we may 

 note others which are common to all the members of the group. 



The body is depressed. There are 5 pairs of gill-openings. 

 The dorsal fins, if present, are not preceded by spines and are 

 placed more or less posteriorly, the first never in advance of the 

 pelvics; the anal fin is wanting. The elongate propterygium 

 is directed forwards and may be divided into several segments ; 

 it bears a considerable number of radials ; the backwardly directed 

 metapterygium is similar to the propterygium ; the comparatively 

 small mesopterygium bears relatively few rays ; increase in length 

 of the region of articulation may or may not be accompanied by a 

 corresponding elongation of the mesopterygium. In the former 

 case (Ilhinobatidas, Raiidse) one or more radials become distinctly 

 attached to the pectoral arch between mesopterygium and meta- 

 pterygium ; in the latter (Dasybatidse) the mesopterygium may 

 segment into two or three pieces *. 



The mixopterygia (text-fig. 117, C, p. 739) show the following 

 peculiarities : — The axial cartilage ends in a rather broad, fiat 

 process with a rounded edge ; it is separated from the basiptery- 

 gium by from two to four proximal segments. The accessory 

 cartilage (wanting in Narcine) is radial-like, but more or less 

 flattened ; proximally it is attached to the first axial segment and 

 distally to the axial cartilage proper. One or more covering pieces 

 are developed and there is a special glandular body in the glandular 

 sac. 



Division 1. Narcobatoidei. 



Paired electric organs between the pectoral fins and the head. 

 Bostral cartilages paired or branched. Prseorbital cartilages greatly 

 expanded, reticulated or branched, extending forwards to the 

 anterior margin of the snout, articulated on each side proximally 

 to a process of the upper or anterior wall of the nasal capsule and 

 distally to the anterior end of the propterygium (text-fig. 122, B). 

 Suprascapulse united above the vertebral column (text-fig. 123, A, 

 p. 754). 



Family Torpedinid^, 



Dorsal fins two, one or none, if present situated on the tail ; 

 caudal fin present; pelvics not notched. Basalia of the dorsal 

 fin in small number (3) ; radials in moderate number (8), simple, 

 of moderate length, not nearly extending to the free edge of the 

 fin. None of the radials of the pectoral fin directly attached to the 



* Comparison of the pectoral cartilages in Dasyhatis and Myliohatis convinces 

 me that this is the true explanation of the structure of the latter. Gegenbaur 

 considered that the posterior segments were formed by the fusion of proximal 

 segments of radials which had become attached to the pectoral arch. 



