Cotylogaster occideutalis n. sp. 615 



mantle cavity of members of the TJnionidae is morphologically the 

 exterior of the body I think we can hardly regard the conditions sur- 

 rouiuling Cotylaspis in the position in which it usually occurs as be- 

 ing the same as those surrounding ectoparasitic animals generally. I 

 should hardly Cüusider this diti'erence of more significance than the 

 geographica! one — one species occurring in N. America and the 

 other in Africa. But, however, that may be I think we can hardly 

 consider differences in habit as having equal systematic value with 

 morphological ditierences. All that we positively know of the mor- 

 phology of the two species iudicates a very close relationship. The 

 difterences which questiouably exist are of the uature of at most 

 specific ditferences. I cannot regard the sum of these as constituting 

 a valid generic distinction. Had Monticelli treated Leidy's genus 

 Cotylaspis with as much consideration as Kofoid is iuclined to give 

 to MoNTicELLi's Flatyaspis I think we may safely say the latter genus 

 would not have been proposed. Kofoid's rehabilitation of Leidy's 

 Cotylaspis leaves in my opinion, no room for Monticelli's Platyaspis. 



The genus Stichocotyle of Cunningham was refused recognition 

 by Monticelli ('92) on the ground that only the larva was knowu 

 and this might not improbably prove to be the larva of Macraspis. 

 Since that time Odhner ('98) has discovered the adult of Sticho- 

 cotyle and fully established the connection between it and the larval 

 form and also its specific distinctness from Macraspis. His obser- 

 vations taken in connection with what was before known concerning 

 the larva (Cunningham '87, Nickerson '95) make the life history of 

 this form better known at present than that of any other Aspid- 

 obothrid. In my paper (Nickerson '95) on the larval Stichocotyle I 

 suggested the possibility that the adult when found might resemble 

 Macraspis sufficiently to Warrant the putting of both forms in the 

 same genus. The maiu facts of the internal anatomy of Macrasjns 

 have since become known thro' the investigations of Olsson ('96) and 

 Jägerskiöld ('99) and although coraplete descriptions of the adult 

 Stichocotyle are not yet published enough is known from the papers 

 mentioned above to Warrant the Statement that the genus established 

 by Cunningham should be retained for the latter form, The chief 

 difierences between the two genera as far as known at present are: 



Macraspis Stichocotyle 



Single Compound ventral sucker. Ventral suckers numerous — mostly 



distinct. 

 Marginal sense organs present. Marginal organs lacking. 



