234 



Mr. E. J. Bles. On the Openings in the 



placed together under A, and the species without them together 

 under B. The species under B all possess abdominal pores. Under 

 A, on the other hand, there is no such uniformity as regards the 

 pores. We have here a fairly complete series of species ; beginning 

 with forms without abdominal pores like Cestracion, passing to forms 

 like Scy. stellare, which acquire pores late in life and may occasion- 

 ally fail to do so ; we then come to the Scy. canicula group, where 

 pores are found at the stage of sexual maturity, but where they may 

 be acquired still later or sometimes not at all ; and, lastly, there is a 

 fourth group, that of Acanthias vulgaris, where the pores appear at 

 an early age, towards the end of embryonic life, and seem to be 

 invariably present. These four groups have one character in 

 common : the nephrostomes remain open in the adult. In this 

 they differ from the species under B, which close the nephrostomes 

 early in development, and then, like Group 4 of Series A, and like- 

 wise at an early age (Carcharias during foetal life), open abdominal 

 pores. 



To some of the species in Table I no place in Table II can be 

 assigned until more specimens of different ages have been examined. 



It is sufficiently obvious from the list of species in Series B of 

 Table II that abdominal pores are distributed without reference to 

 oviparity or viviparity. 



Table I. 

 Elasmobranchii. 





Segmental 

 tubes. 



Abdominal pores. 





Open. 



Closed. 



Present. 



Absent. 



Sub-Order Selachoidei. 



Fam. 1. Carchariidae. 



a. Carchariina. 



Galeus canis, Bonap 



b. Zygaenina. 



Zygana malleus, Bisso, $ 







+ 

 + 



+ 





c. Mustelina. 



Mustelus vulgaris, M and 







+ 











+ 





Triads semrfasciata, Girard 

 Fam. 2. Lamnidae. 







+ 

 + 





(Fam. 3. Khinodontidae.) 

 Fam. 4. Notidanidae. 



Hescanchus griseus, Grm., % juv. 



Heptanchus cinereus, Gm., ? . . 



+ 

 + 





(or +) 





