804 MR. p. E. BEDDABB AND MISS FEDARB [June 20, 



segments xix.-xxii. ; three of them show only three pairs on segments 

 xix.-xxi. ; one specimen has three papillae on segments xix.-xxi. on 

 the right side, and on segments xx.-xxii. on the left, while on both 

 remaining forms one has only three papillae at the right, the other 

 one at the left side of the body on segments xix.-xxi." 



The spermathecse also are varied. Only one individual had a pair 

 in each of segments vi. and vii. Four others had no spermathecse 

 at all. In the three others they were asymmetrical and as many as 

 3 and 5 on one side of the segment. 



As our series of variations is more extensive than those recorded 

 by Dr. Horst, we think that it will be worth while to record them. 

 It is conceivably a noteworthy point that our specimens come from 

 the New World, but we do not wish to lay more stress upon this 

 fact than it will bear. 



The present communication deals with 18 mature examples of an 

 earthworm from British Guiana, which were received through the 

 kindness of Mr. Cecil Lilley, and which show conclusively that 

 there is no need for the retention of the species P. acystis. It 

 seems to be undoubtedly identical wdth P. biserialis. 



The worms were so much softened by the spirit in which they 

 were preserved that it seems to be of no great use to give an 

 attempt at accurate measurement of length. To mention that one 

 specimen actually measured 475 mm. would be to give quite an 

 erroneous idea of its size when in a moderate degree of contraction. 

 It may be taken that these individuals were of about the same 

 dimensions as the examples examined by I lichaelsen. 



The number of segments in a fair-sized specimen was 190. 



The dorsal pores, as in Michaelsen's specimens, commenced 

 between segments xii./xiii. 



The setse of this species, as already mentioned, are remarkable 

 for the fact that the two on the ventral median line on either side 

 of the nerve-cord are considerably larger than the others. Pm^ther- 

 more, the setae of the anterior segments are all or most of them 

 larger than those on the posterior segments, and in segments v.-viii. 

 the four most ventral setae are larger than the (others and increase 

 progressively up to the 7th. The setae appear to be, for the 

 most part, absent upon the clitellum ; but in one specimen, at any 

 rate, there was a single seta on each side of the middle A^entral 

 line of the sixteenth segment. The qaestion of setae upon the 

 clitellar segments of Perichceta is one which requires a renewed 

 consideration. It has been common to use the presence or absence 

 of setae as of specific value, but it seems to be possible, from the 

 variations which have been recorded in some species, that setae are 

 really not finally present upon the clitella of many species where 

 they exist for a short period after the formation of the clitellum. 

 As development proceeds they drop out. 



In a selected series of segments the numbers of the setae are as 

 follows — ii. 42, V. 60, x. 76, xii. 64, xvii. 55, xix. 60, xxiv. 60. 



A few may of course have been omitted owing to their having 

 fallen out and their apertures not noticed. 



