STATISTICAL AND ICHTHYOLOGICAL INVESTIGATIONS. 



175 



2. Syngnathus rostellatus, Nilss. 



The reasons for separating this common and widely -distributed 

 species from S. acus, Linn., are the following : — 



J . The differences between the two forms are so distinct and of such 

 a degree that they are not likely to be due to differences of age. 



A comparison between twenty-two individuals of the former species 

 and forty-seven of the latter, gives the following ranges of variation : — 



Ann. corp. 

 Ann. caud. 

 Siimma ann. 

 Ann. p. dors. 

 Rad. p. dors. 

 Ann. Ijurs. gen. 



Observed Total Length 



2. The individual variation in the number of body rings in the 

 Syiujnathidac (corresponding to the individual variation of abdominal 

 vertebras in other fishes) is a very low one. {Si2Jho7Wstoma ti/pJile, Linn. 

 Syngnathus ■pelagicus) 



3. The fully-developed young in the brood-pouches of the males of 

 both forms differ by the same number of rings as the adult, as well as 

 differing in their total lengths. (They are about 1"5 cm. and 2o cm. 

 respectively.) 



4. Sexual maturity has been observed in individuals of aS^. rostellatus, 

 Nilss., above 11 cm. long, in S. acus not below 30 cm. 



5. Cross-breeding between the two forms seems unlikely, in conse- 

 quence of the difference of the sizes of the eggs and brood-pouches in 

 the two cases. 



At Plymouth I obtained S. rostellatus, Nilss., from Cawsand Bay and 

 from the Yealm Eiver; ;S'. acus from the same places and from the 

 Hamoaze. I also possess specimens of S. rostellatus, Nilss., from the 

 western Baltic, tlie North Sea, and the Mediterranean. Through the 

 kindness of Mr. E. W. L. Holt 1 was also able to compare some 

 specimens from the lliver Humber. 



