ON TEMNOCEPHALA. 



279 



On Ternnocephala, an Aberrant Monogenetic 

 Trematode. 



By 



William A. Has well, 1*1. A., B.Sc, 



Lecturer on Zoology and Comparative Anatomy, Sydney University. 



With Plates XX, XXI, and XII. 

 A 



Historical. 



About the year 1849 Gay discovered, in the environs of 

 Santiago, on the surface of certain crayfishes, a leech-like 

 animal, which, in a letter to Blainville, he described briefly 

 under the name of Branchiobdclla chilensis. 1 The genus 

 Branch iobdel la was first instituted by Odier, and, though 

 apparently the name was applied by him to a species of the 

 genus Branchellion of Savigny, it has been very generally 

 adopted since for an external parasite of the fresh-water crayfish 

 of Europe — the Branchiobdclla astaci of Rudolphi. 



Branchiobdella astaci, as is well known, is a well-marked 

 Leech ; it has an elongated body composed of about eighteen 

 distinct rings, with an anterior and a posterior sucker, an anal 

 aperture above the posterior sucker, and a median ventral 

 nerve-cord. In Gay's 'Zoology of Chile/ 2 Blanchard described 

 Gay's species under the name of Ternnocephala chilensis, 

 recognising that the differences between it and Branchi- 

 obdella astaci arc too great to admit of both species being 

 placed in one genus. " Las Temnocefalas se distinguen ami 



1 I am not aware that the letter has been published, but it is quoted by 

 Moquin-Tandon in the ' Monographic des Hirudincs,' p. 300. 



2 ii, p. 51. 



