138 DR. W. B. BENHAM ON [Feb. 16, 



belongs to Perrier's genus, and name it after that zoologist. I shall 

 reserve certain histological points for later consideration. 



Plutelltjs perrieri, n. sp. 



It has a length of 2 inches (50 mm.) and a comparatiTely great 

 diameter — namely a little more than i inch (4 mm.) ; the length of 

 the clitellum is 4 mm., and the distance from its anterior margin to 

 the tip of the prostomium is 7 mm.^ There are 126 somites in the 

 specimen which remains uninjured ; they are all well marked and 

 are only obscurely annulated. The two extremities of the worm are 

 rounded, obtuse, and not noticeably attenuated, and at the posterior 

 extremity the body is slightly dilated. 



The prostomium is distinct and completely dovetailed into the 

 buccal somite, as it is in P. heteroporus. 



The clitellum, when the worm is fully developed, extends all round 

 the somites xiii. to xviii., with the exception of the median ventral 

 region of the last somite and a short portion of the first somite. 



The intersegmental grooves are entirely obliterated and the anterior 

 and posterior boundaries are very sharply defined. In the specimen 

 dissected, where the clitellum was not so fully developed, the 

 ventral surface of the somites was less glandular and the grooves less 

 olditerated than in the entire specimen, and a pair of papillae exist on 

 somite xviii. between the chaetse " 1" and "2." In the fully matured 

 form, the glandular modification of this somite extends ventrally so as 

 to become continuous with these papillae, which are then no longer 

 evident. 



[In P. heteroporus the clitellum is also complete, occupying 

 somites xiv. to xvii., but overlapping the anterior part of somite xviii.] 



The chcetcB, eight in number, are isolated ; the ventralmost — con- 

 stituting the series of ch^tae " 1" — on each side is close to the 

 middle line ; if the space between " 1" and " 2 " be taken as the unit, 

 represented by S, the space between the ventral chaetae of the two 

 sides is IS, that between the second and third is lg>S, that between 

 "3" and "4" is 2S, and the dorsal area, between the dorsalmost 

 chaetSB of the two sides, is 5/S ; the chaetae " 4 " lie dorsally 

 (Plate VII. figs. 2 and 4). Posteriorly the space " 1-2 " is slightly 

 greater than it is anteriorly ; and anteriorly to the clitellum, space 

 l-I is less than it is posteriorly. 



[In P. heteroporus the chaetae are equidistant, but posteriorly the 

 dorsal and ventral spaces are a little greater than the lateral spaces, 

 and spaces 1-2 and 3-4 are a little less than anteriorly.] 



The chaetae themselves are of the usual lumbricid form, without 

 ornamentations ; there are no modified, copulatory chaetae of any sort. 



The nepliridiopores are not visible externally in my specimens, 

 which are very well preserved, and the segments probably a good 

 deal closer together than in life ; but I find from my longitudinal 

 sections that they have the following arrangement (Plate VII. figs. 2 

 & 4) : — The first pore lies on the anterior margin of somite iii., and, 



^ These figures for P. hetcroponts are 15 cm. as length of body, 6 rum. as 

 length of clitellum, and 4 nun. as its distance from the extremity of the body. 



