44 BNTOZOA. 



organs, of wHch there are six in all, supports a single scimitar-shaped 

 homy piece designed to strengthen the sucking and grasping action 

 of the disk ; and the latter organ consists of a strong, muscular, 

 spherical cup, whose margins are capable of being folded some- 

 what after the fashion of a double nightcap. As regards the 

 visceral arrangements of this genus, it is unnecessary to enter into 

 minute details, but I may briefly remark that the digestive coeca are 

 rather irregularly ramose, whilst, in other respects, these organs 

 conform to the general trematode type. The species here 

 described was, in the first instance, discovered by Kuhn attached 

 to the gills of a dog-fish (ScilUum catulus), but it has since been 

 found as an ectoparasite upon other marine fishes. Its ova carry 

 two filamentary "holdfasts," one at either extremity of the 

 chorion. 



Genera. — Folystoma, Rudolphi ; = Hexacotyle, De la Roche ; 

 = Plagiopeltis, Diesing ; = JBiexabothrivmi, Nordmann ; Pledano- 

 phorus, Diesing; = Pledanocotyle, Diesing; Diclibothrium, Leuc- 

 kart; = Hexacotyle, Nordmann; := Dvplohothrium, Leuckart; 

 Solenocotyle, Diesing ; Octobothrmm, Leuckart ; = Placoplectanum, 

 Diesing; = Odostoma, Kuhn; = Odopledanum, Diesing; = 

 Mazocraes, Hermann; = Odocotyle, Diesing; = Dididophora, 

 Diesing ; = Gydocotyle, Schultze ; = Discocotyle, Leuckart ; 

 Axine, Abildgaard ; = Heter acanthus, Diesing ; Onchotyle, Diesing ; 

 Diplozoon, Nordmann ; = Diporpa, Dujardin ; Gruhea, Diesing ; = 

 Pleurocotylus, Gervais and Van Beneden ; Gotylaspis^ Leidy ; Aspi- 

 docotyle, Diesing ; Aspidogaster, Von Baer. 



Gyrodadylidce. — As a fifth family of Trematoda, I here bring 

 together those singular ectoparasitic creatures known as the Gy- 

 rodactyles, along with an apparently closely allied genus to which 

 Van Beneden has apphed the title Calceostoma. The Gyrodactyh 

 have hitherto been classed with the Polystomidge, but one would 

 think that the absence of several suckers would be alone sufficient 

 to justify a separation. Amongst the characters which stand out 

 most prominently are those having reference to the presence 



