MUSEUM OF COMPARATIVE ZOOLOGY. 187 
tral cirrus. The final segment is destitute of lateral spines and has two long 
anal cirri. 
The mandibles can be easily seen through the body walls, and are well devel- 
oped in this early condition of the worm. The stomach extends from the sec- 
ond to the third or fourth body segment, and the intestine is a small straight 
tube. The body is transparent, colorless, or of a slight green or brownish 
tinge. 
Pilidium recurvatum sp. nov.* 
Plate V. 
One of the most interesting of the worm larve found at Newport is a Pili- 
dium which has many structural relationships to Tornaria, the larva of Balano- 
glossus, and to Actinotrocha, the young of Phronis. This Pilidiwm is the nurse 
of a worm which has many resemblances to the Nemertean genus Lineus. 
As it differs widely from any known species of Pilidiwm, I have given it for 
convenience in description the provisional name of P. recwrvatwm on account 
of the characteristic curvature at its upper end. The new Pilidium from New- 
port differs very greatly from any known species of this genus. The upper 
hemisphere of the larva is not greatly unlike that ot the other species of the 
genus Pilidiwm, but the outlines of the lower hemisphere are so very exceptional 
that it is almost impossible to homologize it with any known forms. P. recur- 
vatum has not the two circular lappets of P. gyrans, nor the arm-like bodies of 
P. brachiatum and P. auriculatum. The ring of cilia about the lower hemi- 
sphere of P. recurvatum is not represented in any other species of Pilidiwm, 
unless we homologize it with a part of the ring of large cilia on the rim of 
the body and along the edges of the circular oral plates of P. gyrans. 
The youngest form of P. recwrvatum which was taken is represented in 
Plate V. Fig. 1. The body is elongated, egg-shaped, with the upper end re- 
curved and the mouth downward. The walls are of glass-clear transparency, 
but always in the same condition, so that it is impossible to tell its age, although it 
seems to be immature. This worm is of very dark brown or black color, especially 
in the anterior body segments. The head is small and of spherical shape, although 
totally destitute of appendages. The eyes are large rounded bodies, two in num- 
ber, deeply sunken into the anterior dorsal cephalic walls. They have a brownish 
or chocolate color. 
The first six (?) anterior body segments have a black color, and bear small per- 
manent sete. The following segments of the body are furnished with very long 
spines, which are very conspicuous as the worm swims in the water. The posterior 
body segments resemble the anterior in bearing very short spines, although their 
color is lighter brown and contains more yellow than those of the middle body 
region. There are in all over fifty body segments. One or two specimens of this 
worm are taken each year, generally by night fishing. 
* This nomenclature is provisional. The larva is not a true Pilidium. 
