THE NEMERTEANS OF PORTO RIOO. 
227 
varying thickness, but on the whole somewhat surpassing the glandular layer in volume. The 
muscular layers of the body walls are as in other species. 
The oesophagus is surrounded with numerous blood spaces of larger area than in most species. 
The cerebral sense organs are remarkably voluminous, and lie immediately behind, and in close 
contact with, the dorsal ganglia. Anteriorly they extend forward beneath these ganglia, and their 
anterior extremities lie externally in the angle between the dorsal and ventral ganglia. A small canal 
leads from the anterior extremity of each sense organ obliquely forward and opens to the exterior in 
a shallow groove on the ventro-lateral aspect of the body a little in front of the anterior portion of the 
brain. The buccal nerves are very large. 
The proboscis is small, and the proboscis sheath short. The muscular and other layers in each 
are quite as in related species. 
4. Micrura leucopsis, sp. nov. 
A rather compact species, 50 to 100 mm. long and about 4 mm. wide. The head is marked off 
from the succeeding portions of the body, when contracted, by a narrow constriction extending 
entirely around the body. The head is variable in shape and is acutely pointed or broadly rounded, 
according to the state of contraction. The mouth is of large size; the lips are whitish in color. The 
cephalic furrows are of moderate length, reaching back to the annular constriction when contracted. 
The mouth lies a little farther back than the posterior ends of the cephalic furrows — not reaching 
forward to the annular constriction. The body is somewhat flattened both above and below, but the 
lateral margins are rounded. The caudal cirrus is colorless and of moderate size, or rather small. The 
proboscis is colorless, of moderate size. 
Color . — As preserved in formalin the color is homogeneous slaty blue or purplish, with a tinge 
of gray, except on the head. The color of the head is similar to that of the body, but is clearer and 
not so grayish. The tip of the snout, both above and below, is pure white (at least after preservation 
in formalin). This white patch surrounds the proboscis pore and extends backward a short distance 
along the cephalic furrows. No ocelli could be found. It is possible that such are present, but could 
not be detected on account of the extremely dark and opaque color of the body. After standing 2J 
years in alcohol the color is still as dark as after the first month. 
Hucares: Four specimens, one of which is 100 mm. in length after preservation in alcohol. 
In internal anatomy this species presents very few peculiarities. The great abundance of pigment, 
which gives the species its very dark color, is situated mainly in the cutis. It occurs also in lesser 
quantities in the connective tissue among the muscular fibers, and a considerable layer of it lies just 
external to the circular muscular layer. 
The cutis glands are well developed, and extend as a thick layer well down into the outer 
longitudinal muscular layer. 
The brain and cerebral sense organs are as in other species. The dorsal median nerve is 
conspicuous. 
The nephridia rqach forward to the mouth, but do not extend far back into the oesophageal 
region. The nephridial canals are small and profusely branched. There are several remarkably 
narrow efferent ducts on each side, opening on the dorso-lateral aspects of the body. 
[ Linens albongsus, which Verrill has described from Bermuda (Trans. Connecticut Acad., x, 
p. 598, 1900), is widely different from the above, the two species agreeing only in having the tip of 
the head white in color.] 
5. Cerebratulus antillensis, sp. nov. 
As preserved in alcohol the head is pear-shaped and very much flattened; the body is much 
flattened and has thin edges. The cephalic furrows are long and deep, reaching a little farther back 
than the anterior end of the mouth. Mouth of moderate size. Proboscis pore subterminal. A con- 
spicuous pit lies exactly terminal, and this is nearly, but not quite, reached by the cephalic furrows. 
As seen in microscopic sections this terminal pit represents a very highly developed frontal sense organ. 
Color . — In formalin the color of the body is faintly reddish, mottled thickly with brownish on 
the dorsal surface. Under sides and anterior margins of head paler. 
Mayaguez Harbor, Pt. del Algarrobo, in sand or mud, at a depth of 161 to 172 fathoms. One 
specimen, much broken. Length in life was probably 100 to 150 mm. 
