472 REPORT ON ZOOLOGY, MDCCCXLIV. 



of the abdominal acetabulum, and in the numerous papilla?, 

 disposed in a radiating manner on that acetabulum. On 

 this account he names the worm Tristoma hamatum. It 

 is found only on the external surface of the integument of 

 Pleuronectes hippoglossus, whilst the above-named Tri- 

 stomum inhabits only the oral and branchial cavities of 

 Acipenser sturio. Respecting the internal structure of the 

 Phylline hippoglossi we learn little from Rathke, and his 

 figure of this worm is far inferior to the beautiful one by John- 

 ston (Annals Nat. Hist, vol. i, 1838, p. 431, pi. 15, fig. 3), 

 and with which Rathke is unacquainted. Rathke' s state- 

 ment, that the male genital opening is situate at some dis- 

 tance behind the mouth 011 the median line of the abdomen, 

 is incorrect ; it is much rather, as Johnston has very dis- 

 tinctly represented it, and as the Reporter can confirm, 

 placed quite anteriorly near the left suctorial disc, externally 

 on the acute lateral margin of the abdomen, whence a long 

 penis can be traced, passing obliquely to the median line of 

 the body. The two large roundish organs situate in the 

 middle of the body, are undoubtedly the testes, whilst 

 another whitish organ, also visible in the interior, represents 

 either the ovary (keim-blaschen-stock) or a vesicula semi- 

 nalis. 



Rathke (ib. p 242) has described an Octobothrium digi- 

 t at urn as new, but afterwards (Archiv, 1844, Bd. i, p. 259) 

 recognised in this parasite, which he found on the gills of 

 Pleuronectes hippoglossus, the Octobothrium palmatum, pre- 

 viously described by Leuckart in his Zoological Fragments. 

 He has also (Nov. Acta, &c., p. 244) besides this settled 

 the diagnosis of his new genus Peltogaster, instituted some 

 time since, as follows : " Corpus torosum, inarticulatum ; 

 alterum ejus extremum in tubum brevem production, ore 

 amplo, orbiculari, inarmato terminatum ; procul ab ore 

 acetabulum rigidum, corneum, discoideum." To the former 

 species, P. paguri, with the following diagnosis : " Corpore 

 oblongo, tereti, alterutrum latus incurvato ; acetabulo in 

 medio ventre," Rathke has added a second species : " Cor- 



