BY J. DOUGLAS OGILBV. 389- 



In the Annals of the Museum of Bvienos Aires for 1868 

 Burmeister described a very curious form under the name of 

 I'etromyzon inncrostomus, and as this Lamprey has no place in 

 the Australasian fauna it may be dismissed here with the remark 

 that it forms the type of a genus Exomegas, Gill (see p. 425), and 

 is very rare, only two examples being known to science, the first 

 having been picked up in the streets of Buenos Aires, and the 

 second collected in the Bay of Monte Video. 



Two years subsequently to the publication of Burmeister's 

 paper the eighth volume of Dr. Giinther's Catalogue of Fishes 

 appeared, and his treatment of the conclusions of previous authors 

 is, to say the least of it, revolutionary; as a commencement 

 Mordacia mordax, Gray, from Tasmania, Caragola Inpicida, Gray, 

 Petromyzon anioandteri, Philippi, and P. acutidenfi, Philippi, all 

 three from Chile, are associated under the common name 

 Mordacia inoi'dax, though the author had at his disposal only Dr. 

 Gray's two original specimens, one of which was in a notoriously 

 bad condition ; even the selection of the generic name was 

 unfortunate, Caragola having a slight precedence over Mordacia, 

 and though, for reasons hereafter stated, I have adopted the 

 name Mordacia, it is not to be expected that all other authors 

 will be equally complaisant,* and we shall, therefore, be cumber- 

 ing our pages with a dual synonym}^, one school of writers adhering 

 to Mordacia while the other as strenuously upholds the claims of 

 Caragola; all which confusion would have been avoided b}' the 

 initial attention to the strict rules of nomenclature. Continuing, 

 Dr. Giinther united Gray's Geotria and Velasia, a conclusion 

 which is not borne out by a more careful examination of the two 

 forms, and announced the occurrence of the latter in New 



* Eigenmanu & Eigenmaiin in "A Catalogue of the Fresh-water Fishes 

 of South America" (Proo. U.S. Nat. Mus. xiv. 1891, p. 24) call the Chilian 

 species Caragola mordax, thus possibly further confusing the synonymy as 

 it is very unlikely that the Australian and Chilian forms are identical, and 

 in view of my own discoveries in regard to the marked ditferences between 

 Velasia and Geotria it is at least possible that both Caragola and Mo7-dacia 

 may be valid. 



