4 28 Mr. R. Southern on the Alciopinse Sfc. 



following to be essential to gephyrocercy : " the posterior 

 part of the tail to have aborted and the interval between the 

 dorsal and anal to have become bridged across by a secondary 

 formation of rays, inserted on basalia and derived from the 

 dorsal and anal fins." Now the caudal fin of Fierasfer den- 

 tatus fulfils all these conditions except that the rays are not 

 inserted on basalia ; this latter condition is one which I have 

 not seen insisted on before ; moreover, Ryder quotes Fierasfer 

 as illustrating his definition of gephyrocercy, and such 

 eminent authorities as Professors L. Dollo * and B. Dean f 

 consider this form typically gephyrocercal. 



According to Mr. Regan's description of the caudal fin of 

 Genypterus, viz. that it possesses two expanded hypurals, 

 this form is undoubtedly homocercal. Since this is so, it is 

 fairly safe to conclude that in the larval stages this fin passes 

 through a heterocercal stage ; but Fierasfer has no hypurals, 

 and according to all records that have been available to me 

 there is no evidence of a heterocercal stage during develop- 

 ment. Again, the caudal fin of Genypterus, being supported 

 by hypurals, is morphologically a ventral fin, while that of 

 Fierasfer is shared by dorsal and ventral rays, and a gap 

 remains between the two halves. For these reasons we are 

 scarcely justified, I think, in considering the caudal fin of 

 Fierasfer to be in a " condition somewhat more specialized 

 than in Genypterus" which implies that they are to be 

 considered in the same category ; on the contrary, it appears 

 to me that Fierasfer has a typically gephyrocercal and 

 Genypterus a homocercal caudal fin. 



LXIV. — A Preliminary Note on the Alciopinae, Tomopteridas, 

 and Typhloscolecidae /v-0//? the Atlantic adjacent to Ireland. 

 By R. Southern, B.Sc., Irish National Museum, Dublin. 



The collection of Polychagta made by the Scientific Staff of 

 the Fisheries Branch of the Department of Agriculture and 

 Technical Instruction for Ireland contains a number of species 

 belonging to the above pelagic families. With the exception 

 of the two species Tomopteris helgolandca and T. septen- 

 trionalis, none of them has hitherto been recorded from the 

 British Marine Area. The list ot species is as follows : — 



* ' Sur la Phylog<5nie des Dipneustes,' 1895. 

 t ' Journal of Morphology,' 1894, p. 102. 



