1903.] NATURAL SCIENCES OF PHILADELPHIA. 723 



The type specimen is 22 mm. long, 2.3 mm. between the tips of the 

 parapodia without setse and .7 mm. in width of body in the middle 

 region. 



The small size of the species might lead to the belief that it is an 

 immature phase of another species, but any doubt as to its distinctness 

 is dispelled by the presence of large numbers of mature ova in the 

 coelom of many specimens. The species occurs occasionally on mussel 

 beds just below low water and was found quite commonly during the 

 latter part of August, both of 1902 and 1903, swimming at the surface 

 of Wood's Hole harbor with other species of sexually mature nereids 

 and syllids. 

 Loimia viridis n. sp. 



In the preserved state the body is rather slender and regularly taper- 

 ing, the thoracic region passing easily into the abdominal without any 

 sudden diminution in size, though the former is circular in cross-section, 

 the latter flattened below and highly arched above. The first thirteen 

 somites are smooth and not annulated, the remaining thoracic and first 

 two abdominal (which are longer than the succeeding ones) strongly 

 but somewhat irregularly subdivided. Apparently there are three 

 primary annuli, the middle one of which bears the parapodia and an 

 irregular zone of sense organs. Each is divided into two or three very 

 short, often incomplete annuli. This condition passes gradually into 

 the typical biannulate arrangement of the middle abdominal somites, 

 in which a somewhat larger posterior ann\ilus bears the parapodia 

 and sensory zone. Toward the caudal end the somites become very 

 short and simple. The anus is small and surrounded by four very short 

 papillae. 



There are nine ventral plates, the first corresponding to somites II 

 to V, the limits of which are indicated by faint grooves, and extending 

 high upon the sides. Successive plates become gradually narrower 

 and longer, the second being three times as wide as long, while the 

 eighth is as long as the width of its anterior and one and one-half times 

 its posterior end. The ninth is narrow, transversely wrinkled and 

 ends opposite the middle of somite XIII. All of the ninth and the 

 posterior half of the eighth are highly vascular. Dorsad of the ventral 

 plates on each side is a whitish, thickened glandular area anteriorly 

 including the bases of the branchiae and nearly meeting on the dorsum. 

 Posterior to the branchiae they quickly become narrowed and restricted 

 to the region of the parapodia and disappear altogether at about XII or 

 XIII. 



The prostomium surrounds the mouth completely and consists of a 



