524 OLIGOCHAETA 



is not stated by Rosa whether this is also the condition of the glands in 'AcantJvo- 

 drilus spegazzinii.' Neither of the worms have penial setae. The position of the 

 calciferous glands and the structure of the spermiducal glands, ally these two species 

 to Ocnerodrilus as has already been pointed out ; and I am disposed to form a 

 separate genus Kerria for them, a genus which has been accepted by Eisen (4) 

 who has added two new species to it. 



The remaining Acanthodrilidae comprise about sixty species ; this is not perhaps 

 an unwieldy number to include within a single genus ; and until recently all these 

 species, that is as many of them as were known — and no new structural characters 

 have cropped up to render a change necessary on fresh grounds — were so included. 

 Though all these species agree with each other in the characters made use of in the 

 definition of the family given above, there is a much greater amount of structural 

 variation among the different species than there is for example in the genus 

 Perichaeta (s. s.), and a very great deal more than in AUolobophora and Lumbricus. 

 This of itself seems to render the subdivision of the genus Acanthodrilus (sensu lato) 

 desirable in order to secure a uniformity of treatment for the whole group. Never- 

 theless, the task is not an easy one. It has been proposed at various times to form 

 the following genera — Trigaster (Benham 3), Benhamia (Michaelsen 13), and 

 Diplocardia (Gaeman 1) ; the name Acanthodrilus being applied to the remaining 

 forms not included in these genera. 



The name Trigaster lankesteri was applied by Benham to an earttworm from the island of 

 St. Thomas, differing from all the species of Acanthodrilus, at that time known, in the following 

 points: — (i) the male pores enclosed by a ring surrounding a deep fossa; (2) clitellum reaching 

 from segment xiii-xl; (3) spermathecae without diverticula; {4) three gizzards present. 



Two years later Michaelsen proposed to include in a genus Benhamia those Acanthodrilidae 

 'which have more than one gizzard, in which the segmental organs are arranged in many tufts on 

 the walls of the segments, and an incomplete (that is, with a ventral gutter-like space) clitellum 

 extends beyond the male generative openings.' As this genus was considered to be merely an 

 extension of Trigaster, the earlier name should, of course, have been retained, and was retained 

 by Benham in his essay on the classification of the group (1), and by myself in a paper of 

 similar scope (26). Benham, in the essay just referred to, defines the genus Trigaster {=Benhamia) 

 as follows;— 



'Setae in four couples, all on the ventral surface; individual setae of each couple close 

 together. 



' Clitellum occupies somites xiv-xl ; complete ventrally only on the first few somites. 



'Spermiducal pores in xviii, and prostate pores in xvii and xix, in a large pit or fossa, occupying 

 the middle of the ventral surface of somites xvii to xx, the margins of which are formed by two 

 papillae. 



'Prostates as in Acanthodrilus. No penial setae.' 



A number of other characters follows, inclosed in brackets which indicates that they are less 

 easy to observe or less distinctive— i.e. more subject to variation from species to species. But 



