482 



OLIGOCHAETA 



This genus, like many others of the Cryptodrilidae, is by no means altogether 

 satisfactory ; but it represents the best that the facts at hand permit of. The 

 presence of three distinct and separate pairs of nephridia in a single segment appears 

 to me to be so remarkable a character that the species thus distinguished from other 

 Cryptodrilidae deserve generic separation. It is, however, only by this character that 

 they can be separated from other species of Cryptodrilus and Megascolides. If the 

 two species, fasiigatus and duhius, were the only two Cryptodrilidae that showed 

 this arrangement of the nephridia, the genus would be much more easily definable ; 

 but T. tenuis and T. mediocris, particularly the latter, differ from those two in 

 a good many particulars, as may be seen by an inspection of the table on p. 448. It 

 may be convenient to recapitulate here in a tabular form the main characters of the 

 four species which I here relegate to the genus Trinephrus. 



Unfortunately, the form of the spermiducal glands is not quite certain in the four 

 species ; Spencer describes them as a ' coiled tubular mass,' but distinctly figures 

 them as of the lobate kind. Fletcher's expression, 'incised glands,' applied to 

 these organs in T. mediocris, seems to indicate that they are lobate. It will be seen, 

 therefore^ that T. mediocris differs from the three other species in having an 

 incomplete prostomium, lobate spermiducal glands, and sperm-sacs in segments ix, xii; 

 and that the three remaining species, as regards these characters, difiier from 

 T. mediocris, but agree with each other. The agreement between T. fastigatus 

 and T. duhius is closest. It would be a relief to find that the nephridia of the 

 species, which I call for the present T. mediocris, were not paired but difiuse. It 

 will be noticed from the tables on p. 448 that the Cryptodrilidae, referred to the 

 genera Megascolides and Cryptodrilus by Fletcher and Spencer, can be arranged in. 

 three parallel series under the two divisions of those with lobate, and those with 

 tubular, spermiducal glands ; in each group are worms with diffuse, paired and 

 three-paired nephi-idia. 



