INVERTEBRATE ANIMALS OF VINEYARD SOUND ETC. 325 



The color is sornetimess bright orange anteriorly, but lighter posteriorly, 

 with a faint dusky or greenish line along the middle. 



Another species, closely resembling the last in form, color, and size, is 

 quite common under stones, and especially in dead tubes of Serpula, near 

 low-water mark. This is the Cosmocephala ocJiracea V., (Plate XIX, figs. 

 95, 95a;) it has numerous eyes on the sides of the head, three or four 

 on each side forming an anterior row parallel with the margin ; the 

 others forming two parallel oblique groups, usually with two or three 

 eyes in each, farther back. On the lower side of the head there is, on 

 each side, an obliquely transverse groove. The color is usually dull yel- 

 lowish-white or grayish ; the anterior part is often tinged with orange 

 and the posterior with ash-gray ; there is generally a distinct paler me- 

 dian line, most distinct anteriorly. It grows to be two or three inches 

 long, when extended. 



Of the Planarians several species are also found creeping over the 

 under side of stones and in the tide-pools. One of the most abundant 

 is Procerodes frequens, which is a very small but lively species, found 

 creeping on the under side of stones near high-water. It is usually 

 about an eighth of an inch long, dark brown or blackish above and gray 

 below, and it has two reniform eyes. The Monocelis agilis is still smaller, 

 elliptical, with only one median eye ; its color is dark brown or blackish . 

 By some writers this genus is placed among the Xemerteans. Two 

 larger species of this group are also occasionally found on the under 

 side of stones. One of these, the Planocera nebulosa, (Plate XIX, fig. 

 100,) is usually about half an inch wide and three-fourths long, but may 

 become nearly circular, or may extend into a long elliptical form. It is 

 fiat and thin, with fiexuous edges. Its color is olive-green above, with 

 a lighter median stripe behind, and yellowish green below. The tenta- 

 cles on the back are whitish and retractile. 



The Styloclwpsis littoralis Y., (Plate XIX, fig. 99,) is also frequently 

 found on the under side of stones. It is remakable for having a clus- 

 ter of eyes on each tentacle, other clusters in front of them, and two or 

 more rows of eye-spots around the margin, especially in front. Its color 

 is variable, but usually greenish, greenish yellow, or bro svnish yellow, 

 often reticulated with flesh-color ; there is generally a pale median streak 

 posteriorly. The eggs were laid July 12th in large clusters, composed of 

 many small white eggs closely crowded together, side by side, and at- 

 tached to the surface of the glass jar in which they were kept. 



There are also representatives of the " round worms," or Nematodes, 

 to be found beneath the stones and among the roots of algse, hydroids, 

 &c. The commonest of these is, perhaps, the Pontonema marinum (Plate 

 XVIII, fig. 94.) This is a small, very slender, smooth, white, round worm, 

 tapering to both ends, and very active in its movements, constantly coil- 

 ing itself into a spiral and again uncoiling itself. Its head is furnished 

 with about six minute cirri ; in the male the tail is short, narrow, nearly 

 straight, but one-sided, rapidly tapering, and subacute ; in the female 



