250 BRITISH FRESHWATER FISHES 



larger series of specimens than I have seen it will be 

 impossible to say how many races or subspecies are 

 definable or whether any of them deserve to rank 

 as distinct species. The number of fin-rays varies 

 considerably in different localities, and so does the 

 development of the lateral plates ; one of the most 

 remarkable forms is that which inhabits the tributaries 

 of the Black and Caspian Seas (P. platygaster\ which 

 resembles the Three-spined Stickleback in that the 

 fourth to the seventh plates of the complete series, 

 near the ascending process of the pelvis, are the 

 most developed, whereas Ten-spined Sticklebacks 

 from other parts of the world have the anterior 

 plates not much deeper than the others when the 

 series is complete, whilst the posterior plates are the 

 most persistent. 



In Western Europe the Ten-spined Sticklebacks 

 are either entirely naked or have a few small plates 

 bearing a keel on each side of the caudal peduncle ; 

 all the British and Irish specimens I have seen agree 

 with those of France and Belgium in having the 

 spines much smaller than in those from Scandinavia; 

 the correct name for this short-spined form, if it be 

 recognized as a distinct race, is Pygosteus Icevis. 



In examples from various parts of the British 

 Isles I count eight to eleven spines and nine to 

 twelve soft rays in the dorsal fin, and one spine and 

 eight to eleven soft rays in the anal. Specimens 

 entirely lacking the pelvis and pelvic fins have been 

 taken at Tipperary and Edgeworthstown in Ireland ; 

 of thirteen captured by Day at the latter place eleven 

 showed this peculiarity. 



The coloration of the Ten-spined Stickleback 

 varies considerably, but is usually a greenish olive, 



