384 PROCEEDINGS OF THE ACADEMY OF [May, 



usually 5 anteriorly and 2 to 4 posteriorly. The setse are all small and 

 of the usual form, except that their tips are curiously variable (fig. 29). 

 As the setse were studied only under the rather unfavorable conditions 

 presented by alcoholic material, it is uncertain how far this may be due 

 to wear. Many of the setse are undoubtedly broken, but those figured 

 appear to be intact. In some the tips are deeply bifid and the points 

 long and acute; others, especially in the posterior dorsal bundles, have 

 the upper or distal point more or less reduced, and still others have a 

 mere apical notch or are apparently entire. 



The coelomic corpuscles are very numerous and about .012 mm. in 

 diameter, with opaque white granules smaller and more numerous 

 than those of M. glaber. 



In internal anatomy this species closely resembles M. glaber, from 

 which, however, it is easily distinguished by the single spermatheca 

 (fig. 34) which opens in the median line of the furrow ^^, and is usually 

 folded on itself transversely. The atria (figs. 32, 33) also differ in that 

 they join in the middle line before opening into the bursa by a single 

 small pore raised on the summit of a papilla. It will thus be noticed 

 that the primitively strictly paired character of the reproductive organs 

 has been departed from more widely in this than the other species. 

 The prostate and other regions of the male ducts are otherwise as usual. 

 An anterior sperm sac extends through IX, a posterior through XII 

 and XIII, and an ovisac to XVI. The vascular system presents the 

 characteristic valvular and chambered vessels and integumental 

 plexus. The brain (fig. 31) is slender and the anterior lobes much 

 elongated. Xephridia are of the character belonging to the genus, but 

 are slender and elongated and the nephrostomial lip especially narrow 

 and prolonged. 



This species has not been found abundantly anywhere. Occasional 

 examples occur with the larger tubificids and with Lumhricillus , but 

 it appears to prefer more gravelly shores and the neighborhood of 

 beach grass, among the roots of which it may be found. In a few cases 

 larger numbers were found living gregariously beneath stones at half- 

 tide on the south shore of Naushon. It is quite probable that it has 

 often been mistaken for the young of M. glaber or even of LumbricilluS' 

 Tubifex irroratus (Verrill). PI. XXXII, figs. 7-li. 

 Clitellio irrorata Verrill (in part), 1873. 



The length of this slender species seldom exceeds 30 mm., but the 

 number of somites may ecpial 90. Most of the examples found in the 

 vicinity of Wood's Hole are not fully mature, and are from 15 to 17 

 mm. long, with about 70 somites. The prostomium is more acute than 



