l8o KOFOID. [Vol. II. 



States, having been found by Leidy ('57 and '58) on Anodoiita 

 fliiviatilis and laciistris^ and by the writer, at the Illinois 

 Biological Station, on Unio alatiis, anodontoides, confragostis, 

 edentulns, elegaiis, gracilis, katJiarinae, ligavicntinus, rectus, tu- 

 berculatus, and on Anodoiita corpiilenta. Unlike Aspidogaster, 

 it is an ectoparasite, being harbored in the mucus upon the 

 surface of the host, upon the foot, the gills, and especially in 

 the region of the axil and along the line of attachment of the 

 inner gill to the body. 



Ever since the publication of the original description of 

 Cotylaspis there has been some question as to the standing of 

 the genus founded to receive this one species; and, indeed, the 

 validity of the species itself has been questioned at times. 

 European helminthologists have assigned it various positions 

 in the system, and have even reduced it to a synonym of 

 Aspidogaster concJiicola. This uncertainty and the resulting 

 confusion in synonymy seem not to be due to the lack of illus- 

 trations and to the nature of the original description, for this, 

 though brief, was concise, and accurate as far as it went, quite 

 as full, indeed, as many specific descriptions by helminthologists 

 of both continents at that day. It was rather the result of an 

 opinion hazarded by Leidy ('58) that Aspidogaster and Cotylaspis 

 might possibly represent " two different stages of existence of 

 the same animal." 



During the last four years the writer has had in course of 

 preparation a paper on the structure of this interesting trema- 

 tode. (See Forbes, '96.) It is the purpose of the present note 

 merely to set forth the grounds on which Leidy's original de- 

 scription of the species is entitled to recognition and to discuss 

 the synonymy briefly. 



The first reference to this unique little trematode is in a 

 brief note by Professor Leidy ('57) in the report of the proceed- 

 ings of the Academy of Natural Sciences of Philadelphia for 

 the meeting held Feb. 17, 1857. In the report of that meeting 

 the recorder states that " Dr. Leidy made the following obser- 

 vations on etitozoa found in the Naiades." (The italics are 

 mine.) Strictly speaking, however, Cotylaspis insignis is an 

 ectoparasite, as above stated, being found, as the note proceeds 



