ON THE ANGUILLULID^. 135 



curved, tooth-like projections from its inner surface. CEsophagus not distinctly 

 muscular, cylindrical, and almost uniform in size ; surrounded by a distinct ceso- 

 phageal ring. Intestine mostly covered with olive-coloured particles, having a 

 tessellated arrangement. Vulva at centre of body, or occasionally at posterior third. 

 Uterus symmetrical or unsymmetrical. Spicules two, with or without a single 

 accessory piece. Ocelli mostly wanting. JSxeretory ventral gland simple, tubular, 

 extending from the anterior third nearly to the termination of oesophagus. Lateral 

 canals often distinctly cellular. 

 Movements active. 



This is not quite so natural an assemblage as those presented by some of the other 

 genera, even after the freshwater species formerly included by Dujardin have been 

 transferred to the genus Mononclms. In some members of this genus Oncholaimus the 

 vulva is posterior, and the uterus unsymmetrical ; and in some males also the spicules 

 are solitary, whilst in one at least, 0. vulgaris, there is a large and well-developed 

 accessory piece. Owing to my not having found in several cases both the male and 

 female representatives of the same species, I am unable to say, from my own observa- 

 tion, whether these alterations in the male and female organs are generally coincident, 

 and constant enough to enable the species to be ranged under two distinct subgenera ; 

 and, unfortunately, the details concerning the anatomy of those discovered by other 

 observers are too scanty to afford any assistance in the solution of this question. In 

 two species also, O. fuscns and 0. alhidus, I have been unable to detect the usual 

 oesophageal ring. 



1. O. VTJLGABis, n. sp. (Plate XI. figs. 126-128 a.) 



Female, length ^", breadth yas"- 



External Characters. — Body elongated, cylindrical, tapering very slightly at extre- 

 mities. Sucker well developed, with three large sucker-tubes occupying nearly the 

 whole of the cavity of body posterior to anus. Head truncate, with a circlet of 4-G 

 short, stout setse, and a few smaller ones scattered over anterior part of body. Integu- 

 ment thick, with an appearance of longitudinal markings two" apart ; integumental 

 pores distinct in mid-dorsal and ventral regions. 



Fharyngeal cavity -^" long by -g^" broad, having three strongly marked, slightly 

 curved teeth projecting into cavity. (Esophagus about ^th of total length, nearly uniform 

 in size, having three longitudinal rows of pigment-granules ; embraced at termination of 

 anterior tliird by an oesophageal ring. Intestine broad, having a thick coating of olive- 

 coloured hepatic granules, enclosed in cells, and presenting a distinct tessellated arrange- 

 ment. Anns TTi" from posterior extremity. Vulva slightly posterior to middle of 

 body. Uterus bifid. Excretory ventral gland opening close to the oesophageal ring. 

 Lateral canals distinct, cellular. 



Male, length -^q", breadth •^". 



Anus 2To" from posterior extremity. Spicules rather wider at middle, and tapering 

 towards extremities, y9o" long. Accessory piece single, somewhat triangular, 4^4" long 

 by g-g-g-" broad at the base. A large mid-ventral prominent sucker T54" above anal c^eft. 



