1905.] NATURAL SCIENCES OF PHILADELPHIA. 395 



moist spots on farm lands on Martha's Vineyard, where it could readily 

 be introduced in the large quantities of eel grass that are annually 

 spread for fertilizer. About Wood's Hole it also lives in damp, sandy 

 woods and on the shores of fresh-water ponds, especially of one that 

 formerly was connected with the Sound. Whether this particular 

 species originated on the strand and migrated landwards or vice versa 

 is not apparent. Its wide distribution along the shore, however, may 

 be accounted for by the ease with which it could be transported in 

 masses of eel grass attached to floating logs, or by clinging to the feet 

 of migrating shore birds. The same influences would affect Lumbri- 

 cillus, but not the various species of tubificids, which burrow in the 

 mud or conceal themselves beneath stones. As a consequence many 

 of the latter appear to occur quite locally. 



Enchytrceus albidus may be easily recognized among our littoral 

 species by its milk-white color and nearly straight, internally hooked 

 setae. 



Lumbricillus agilis sp. nov. PI. XXXIII, figs. 23-28. 



The length of fully extended mature worms is about 16 mm. or less, 

 the greatest diameter is .4 mm., and, owing to the relatively stout ante- 

 rior and slender, tapering posterior parts, the general form is distinctly 

 clavate, particularly in fixed examples. Considerable variation in the 

 number of segments has been observed, ranging from 30 to 48, 47 being 

 a very frequent number in breeding examples. The prostomium is 

 short, blunt and verrucose, and possesses a distinct cephalic pore a 

 little behind the apex on the dorsal side. The spermathecal pores are 

 inconspicuous slits facing laterally in the furrow -^j and the sperma- 

 ducal pores are rather conspicuous simple or usually trifid slits in the 

 position of the absent ventral setae of XII. In preserved worms they 

 are usually on the apex of the everted male bursa. The female genital 

 pores are visible only in sections. When fully developed the clitellum 

 is thick and conspicuous and extends completely around somites XI 

 and XII. Anteriorly the somites increase in diameter and length to 

 the genital region, but are always short ; posteriorly they taper rapidly, 

 and are slender and divided into 3 annuli, of which the middle one bears 

 the setae, and each of which may be further divided into 2 or 3. 



As usual in the genus, the setae are of a gently sigmoid form with 

 rather acute, slightly hooked tips and a slight thickening at the junc- 

 tion of inner and outer limbs. Those of the ventral fascicles (fig. 23a) 

 are decidedly larger than the dorsal ones (fig. 23). Ventral bundles 

 contain from 5 to 8, usually 6, anterior to the clitellum, and from 4 to 6, 



usually 5, posteriorly; dorsal bundles usually 5 anteriorly and 3 or 4 

 26 



