ECTOPAKASITIC TEEMATODES. 273 



the form described by me as Tr. ovale as var. mermis, and the 

 forms described by Verrill and Bell as var. armata* 



Hexacotyle thunnince (Parona et Perugia). 



This is the Octocotyle thunnince of Parona and Perugia ['89]. 

 An examination of a mounted specimen from Prof. Parona in 

 possession of Dr. Stiles, who has kindly allowed me to study it, 

 proves beyond doubt that it must be referred to the genus Hexa- 

 cotyle, as diagnosed in my " Studies " ['94]. The body is, 

 generally speaking, lanceolate, narrow and pointed anteriorly, 

 but broad and tongue shaped posteriorly (fig. 13). The whole body 

 may be divided into three portions : the most anterior slender 

 j)ortion, which is very short and occupies only a little over one 

 eighth of the whole length ; this is followed by a broadened 

 portion occupying roughly about one third of the rest ; then 

 follows a portion of nearly uniform width, which is, however, 

 slightly expanded at the posterior end. There are four pairs of 

 semi-ellipsoidal posterior suckers arranged on the convergent 

 sides of the tongue like portion. They are nearly of the same 

 size, and the most posterior pair are only slightly smaller than 

 the rest, the longer diameter being 0.22 mm.f as against 0.36 

 ram. of the first two pairs. In all the other species of Hexaco- 

 tyle, the most posterior suckers are considerably smaller than 

 the others ; and the peculiarity just mentioned is alone enough 

 to establish the present species. Each sucker is provided with 



* Setti, in his recently published paper ['99] which I received after the above had been 

 written down, has also come to the conclusion that my Tr. ovale is identical with Tr. levé 

 Verrill and Tr. histiophori Bell. As to the opinion of the same writer on the synonymy of 

 2V. mhindum and 3V. coccineum, I can only agree with him ; the differences between the 

 two, enumerated by me ['94, p. 247] are too trivial to be of specitic value. 



t The average of the measurements on the two sides. 



