OF THE BRITISH ISLANDS. 



"3 



exception of a narrow oblique slit, entirely closed over the 

 true eye. When darkness has fully set in, this diaphragm 

 is completely retracted, leaving the eyeball free and gleam- 

 ing like that of a cat or other nocturnal mammal. This 

 phenomenon, observed by the writer of examples in the 

 Brighton and Manchester Aquaria, may be corroborated 

 by an examination of the specimens now on view in the 

 Exhibition tanks. In the Skates, presently described, it will 

 be found that a very beautifully constructed fimbriated 

 membrane takes the place of the diaphragm that covers 

 the eye of the Spotted Dog-fish. 



FIG. 28. — EGG OF SPOTTED DOG-FISH. 



The last upon the list of the Shark tribe is the Monk-fish 

 or Angel-fish (Rhina squatind), No. 214, which in its 

 flattened form, and the great development of the pectoral 

 fins, closely approaches the Rays, the lateral position of its 

 gill -openings, partly hid by the pectoral fins, being how- 

 ever accepted by ichthyologists as of sufficient importance 

 to justify its retention among the present group. Addi- 

 tional evidence in support of its preponderating affinities 

 in the same direction is afforded by its mode of locomotion 

 in the water, observed by the writer of examples in aquaria, 

 and which is entirely that of a Shark, being effected by the 



