1905.] NATURAL SCIENCES OF PHILADELPHIA. 383 



saltness of the water is just barely discernible to the taste, enormous 

 numbers occvu* quite unmixed with other species. If placed in pure 

 salt water of the density found in Vineyard Sound these worms die 

 much sooner than if placed in fresh water, but may be acclimatized 

 to either by gradual changes. In brackish water they have lived and 

 bred in confinement in Philadelphia for seven months, and are now, 

 after this lapse of time, as vigorous as ever. That they are partial to 

 low rather than high densities is shown by the observation that those 

 living on the shores of the Eel Pond at Wood's Hole, at a point where 

 fresh water oozes from the ground below high-water mark, burrow 

 deeper toward the source of the spring when the tide rises and covers 

 their habitation, and come to the surface when it falls. Other favored 

 localities are certain shallow and nearly closed coves where great quan- 

 tities of eel grass and algae accumulate and decay in water diluted by 

 rains. Here under small stones below half-tide mark the species asso- 

 ciates with Tuhifex irroralus and Lumbricillus agilis, though the latter 

 is far more plentiful in the decaying eel grass at a higher station on the 

 shore, and the former prefers the roots of salt grasses growing on more 

 gravelly shores. Though not active in their movements, they are less 

 sluggish than the T. irroralus and far more hardy than that species. 

 From the latter part of July, at least, onward this species breeds, and 

 some specimens brought to Philadelphia continued sexually active 

 throughout the fall and into winter. Wlien breeding they are espe- 

 cially active and congregate in such numbers beneath stones that 

 they impart a quite red color to the surface of the soil when exposed 

 by turning over the stones. 



Monopylephorus parvus Ditlevsen. PL XXXIII, figs. 29-34. 



A second small species of Monopylephorus is referred to the above 

 species, with which it agrees closely in nearly all of the characters 

 recorded in the original brief diagnosis. Further information may 

 necessitate a separation. 



In size and form this species closely resembles Lumbricillus agilis, 

 but its distinctly pink color and the opacity due to coelomic corpus- 

 cles, as well as its more sluggish movements, are a ready means of sepa- 

 ration. Fixed specimens can be distinguished in many cases only after 

 a careful study, especially as sexually mature individuals are infrequent. 



The length is from 8 to 15 mm., the diameter about .4 mm. and the 

 number of segments from 38 to 43. The prostomium is much more 

 slender and pointed than in M. glaber, but the somites are similarly 

 quadri-annulate. The number of setae in each ventral bundle is 3 or 4 

 anterior to the genital region and 2 posteriorly; in the dorsal bundles 



