490 WILLIAM NICOLL. 



distinct genus, and on that account I propose to raise the sub-genus 

 Bucephalopsis to generic rank with B. gracilescens (Rud., 1819) as type. 

 . A comphcation enters here, however, for in 1858 Diesing erected the 

 genus Rhifidocotyle for the reception of the two species G. gracilescens 

 and G. minimum Wagener {nee. Stossich) without designating the type. 

 Stiles & Hassall (1908) have tentatively taken G. gracilescens as the type 

 of this genus, but, as I shall show, G. minimum Wagener is undoubtedly 

 the real type of this genus. 



I am, unfortunately, not personally familiar with Wagener' s original 

 specimens, nor have I had an opportunity of examining any Gasterostomes 

 from the type host, Trigla microlepidota, but a careful study of Wagener's 

 original figure (1852) has suggested to me that G. minimum. Wagener is 

 identified with G. triglae van Beneden, 1870, and with the form which I 

 have described under that name (1909). The most characteristic feature 

 of this species is the highly contractile fan-shaped structure which 

 surmounts the anterior sucker. To both Wagener and van Beneden this 

 structure must have appeared in a very contracted condition and so have 

 escaped observation. Diesing, however, must have been familiar with 

 it and have been influenced by it in his choice of a generic name, hence 

 the highly descriptive combination Rhi'pidocotyle {piTrl?, pl7rioo<;=a. fan, 

 KOTv\t]=a, cup). No more appropriate term could have been invented. 

 At the same time it is remarkable that Diesing should have included in 

 the same genus G. gracilescens, which possesses no such fan-shaped 

 structure. 



There is nothing in the remaining anatomy of either of these species 

 which to my mind bears the slightest resemblance to a fan, and on that 

 account I am convinced that it was the fan-shaped cephalic hood which 

 Diesing regarded as the distinctive feature of this genus. It will thus be 

 necessary to revive the old generic term which Odhner (1905, p. 296, 

 note 3) somewhat cavalierly consigned to the " lumber room of useless 

 names." 



As Gasterostomum has become a nomen nudum the family name 

 Gasterostomidae must be replaced by Bucephalidae, and this family will 

 now include the genera Bucephalus Baer, 1827, Bucephalopsis (Diesing, 

 1855), Rhipidocotyle Diesing, 1858, and Prosorhynchus Odhner, 1905. 

 As Odhner has already suggested, a further separation of these genera 

 appears advisable. I propose to separate them into two sub-families, 

 Biicephalinae, n. subfam._ and Prosorhynchinae, n. subfam. 



The definitions of these sub-famihes are identical with the definitions 

 given by Odhner (1905, pp. 296-7) for the genera Gasterostomum and 



