DANFORTH: NEW PTEROPOD. 
Musculature. 
The general differentiations shown in the musculature of this pter- 
opod are, in addition to scattered muscle fibers in various parts of the 
body, specialized longitudinal bands running between two circular 
muscles, one near the posterior, the other near the anterior ciliated 
ring; the muscles of the head, foot, and parapodia; and those belong- 
ing to the internal organs. The last group presents no features worthy 
of note, the most important of them being the muscles of the ankistro- 
phores, lips, esophagus, intestine, and hermaphroditic duct, all of which 
are mentioned in discussing the organs with which they are connected. 
Of the circular muscle rings mentioned above, the anterior one is 
not well marked oft' from the other strands in the wall of the head and 
is composed of fibers which, like the others, are cross striated. It 
runs around the head, passing just under the cephalic ring of cilia and 
the anterior lobes of the foot. The other ring running below the third 
band of cilia is better defined and composed of smooth fibers. 
The most prominent of the superficial muscles of the body proper 
are three pairs of longitudinal bands, the retractor muscles used in 
shortening the total length of the animal. They all have their anterior 
and posterior attachments near the surface, in the vicinity, respectively, 
of the first, or cephalic, and the third ciliated rings. Their main 
course, however, lies some distance inside the outer body wall, thus 
causing the head and posterior end of the contracted animal to be 
drawn behind the body folds as previously described. These six 
muscles are not well defined throughout but split up posteriorly into 
smaller branches. The two ventral of these longitudinal muscles, 
starting one on either side from a point dorsal to the foot, run backward 
parallel to each other and ventral to the penial gland, then along the 
lower side of the animal medial to the thick body wall till they reach 
the posterior circular muscle described above. The lateral, pair run 
between the anterior and posterior circular muscles at a level a little 
nearer the dorsal than to the ventral retractors, the muscle of the right 
side passing in front just dorsal to the common genital opening. The 
dorsal pair of retractors are situated one on either side close to the 
median line. 
Of the three divisions of the foot, the anterior paired lobes have, 
in proportion to their size, the stronger musculature. They are both 
supplied with fibers running from the anterior circular ring to their 
