3874 The Zoologist — February, 1874. 



One anomalous form, standing, as it were, between the sharks and 

 rays, — the monk, or angel-fish {Rhina squatina), — affords iu its 

 locomotive characters an interesting link further indicating its close 

 affinity rather with the former than with the latter group. The 

 habits of this fish are essentially nocturnal, and throughout the 

 daytime it usually reclines sluggishly at the bottom of its tank. 

 Its depressed body and broadly expanded pectoral fins resemble 

 those of a ray more than a shark, and like the former fish it seeks 

 concealment by burying itself beneath the sand or shingle, ex- 

 cavating a hole with the shovel-Hke action of these broad fins, and 

 thus waits in ambush for passing prey. Immediately the monk-fish 

 rises above the surface of the ground its true aflSnities become 

 apparent, progression being effected entirely by the lateral action 

 of the caudal extremity, as in the sharks, though in a more slow 

 and clumsy manner. The lateral position of the gill-openings in 

 this fish forms its chief shark-like anatomical character, and to this 

 has to be added its viviparous habits. 



In the Batoidea, or ray tribe, onward motion is accomplished by 

 a singular, even, and wing-like action of the broad pectoral fins, the 

 attenuated caudal extremity remaining perfectly quiescent, and 

 serving only to preserve the fishes' equilibrium. Swimming towards 

 the surface of the water, these fish present a most remarkable bird- 

 like aspect, their large flapping fins reminding the observer of the 

 flight of the heron or some other unwieldy representative of the 

 Grallian order, while the slender tail dependent in the rear suggests 

 the characteristic mode in which those birds hold their long legs, 

 while pursuing their course through the more subtle medium which 

 they inhabit. 



Proceeding to the Teleostean group, we find the means by which 

 the same organs are made subservient to the faculty of locomotion, 

 still more highly diversified ; space, however, will only admit of a 

 few selections. 



In the gurnards {Trigla), during rapid movement, all the fins are 

 pressed closely against the body, the broad wing-like pectorals 

 being shut up like a fan, while the fish is propelled swiftly through 

 the water by the vigorous undulations of the tail; when the fish 

 moves leisurely the pectorals are opened to their full extent, 

 acting as balances. In many species, such as the striated gurnard 

 (7". lineata), these fins are brilliantly coloured, reminding the 

 observer," especially when regarding them from above, of gorgeous 



