44 



MARKETABLE BRITISH MARINE FISHES 



is the thornback (Fig. 6), which has spines of various sizes all 

 over its skin : in the starry ray the spines are all large and of 

 nearly the same size ; the cuckoo ray has a circular black 

 mark with yellow lines in its centre, on each wing. Other 

 species are also distinguished by similar small differences. 



Among the bony fishes one division or order is characterised 

 by the following peculiarities : the air-bladder when present, 

 instead of being completely closed and separate from other 

 cavities in the body, is connected by an opening or open tube 



Fig. 5. — The Common Skate, lower or ventral surface. 



with the interior of the gullet or stomach ; the pelvic fins are 

 either absent, as in eels, or are in their original position in the 

 hinder part of the body, as for example in the salmon ; thirdly, 

 the fin-rays are soft and branched, that is to say each ray is 

 composed lengthwise of a series of short pieces of bone united 

 by flexible gristle or cartilage, and also divides towards its outer 

 end into a number of separate smaller branches lying not in a 

 tuft like a brush, but side by side like the ribs of a fan. In 

 certain species however the first ray of the dorsal and ventral 

 fins and of the breast-fins forms a strong undivided spine. 



