378 PHILOSOPHY OF ZOOLOGY. 



(1.) Gill openings Jive an each side. This includes all the 

 species formerly included in the genus Raia of LINNJEUS. 



a. Tail fleshy and of ordinary proportions. The Tor- 

 pedo and Rhinobatus electricus are furnished with electrical 

 organs. The last species ought probably to constitute a 

 separate genus 



17. RHINOBATUS. Snout with the sides angular. R. 

 vulgaris. 



18. TORPEDO. Snout with the sides rounded. T. vul- 

 garis, or Cramp fish. 



b. Tail hard and slender. 



(A.) Tail armed with a long serrated spine. 

 19- TRYGON. Head uniting to form with the pectoral 

 fins an obtuse angle. T. pastinaca. Stinging Ray. 



20. MYLIOBATIS. Head protruded beyond the pectoral 

 fins, which are much produced laterally. M. aquila. 



21. CEPHALOPTERA. Head truncated, and the pectoral 

 fins extending in a process on each side. C. milgaris *. 



(BB.) Tail without the long serrated spine, but fre- 

 quently covered with numerous prickles. The important 

 observations of MONTAGU, point out the necessity of ex- 

 ercising great caution in the establishment of species, and 

 even of genera, in this group, either from the armature of 

 the body, or the form of the teeth f. 



* In Europe, the different species of rays exclusively reside in salt-wa- 

 ter. In the Ganges, however, it would appear from the valuable work just 

 published, " An account of the Fishes found in the Ganges and its Branch- 

 es," by FRANCIS HAMILTON (formerly BUCHANNAN), M. D. 1. vol. 4to, 

 with a vol. of plates, Edinburgh, 1822, that some species nearly allied to 

 the T. pastinaca are common, not only in the estuary, but very far removed 

 from the sea. " For I have seen them (Raia fluviatilis of H.) at Kanpur, 

 more than a thousand miles above the extent of the tide." P. 1. 



f After speaking of the appendages at the base of the tail, he says, 

 :c Accompanying this truly masculine distinction, are series of large re- 



