352 STAITROCEPHALUS. 



Clprd., from Naples, measuring 08 mm., of nine segments, four of which had cirri 

 (branchise). The snout is hoof-shaped, with two eyes, the tentacles arising immediately 

 behind them. Nuchal grooves occur at the posterior edge on each side, and a dental 

 apparatus is developed. The foot is fairly formed and the dorsal cirrus is articulated. 



Genus LXI. — Staurocephalus, Grille, 1855. 

 Anisoceras, Grube. Prionognathus, Keferstein. 



Head rounded, quadrangular or pentagonal, with two articulated tentacles, two 

 palpi, and four eyes. Nuchal organs primitive, ciliated surfaces in direct contact with 

 the exterior (Racovitza). Two segments devoid of appendages. Body with compara- 

 tively few segments. Pygidium with two shorter and two longer cirri. 



Upper jaw with two rows of jaw-plates, the wide halves of the mandible diverging 

 posteriorly into narrower processes. 



Foot long, bifid, the upper division with simple bristles, the lower with compound 

 bristles. Dorsal cirri unequal with a short terminal process. Ventral cirrus arising 

 from the foot, short and simple. 



In transverse section the body-wall (Fig. 76) has somewhat thin dorsal muscles, 



n.c. o.jii. 



Fig. 76. — Transverse section of a nearly ripe male of Staurocephalus rubrovittatus. The ccelom is much distended. 

 d. Alimentary canal, n.c. Nerve-cord. o.m. Oblique muscles. 



but the ventral are more massive in proportion. The ventral nerve-area is large, and the 

 oblique muscles pass downward to be inserted at its sides. At the reproductive season, 

 as in the section figured, the sexual elements largely distend the ccelom, and the muscular 

 layers undergo more or less atrophy. 



One of the most interesting features in the genus is the occurrence of pelagic 

 "swarming" in a species (Staurocejohalus gregarious) from the Tortugas Islands, Florida, 

 as described by A. Gr. Mayer. 1 The entire worms leave the coral rocks, swim at the 

 surface, and discharge the sexual products soon after sunrise, e.g., on July 19th, when the 

 last quarter of the moon falls on July 18th. The author also gives figures of the eggs 

 and larvas. 



G rube's first group contains those in which the palpi (his sub-tentacles) have no 

 terminal segment. It includes the common British species. 



1 A. G. Mayer, < Bull. Mus. Comp. Zool./ Harvard Coll., vol. xxxvi, No. 1, 1900. 



