1907.1 NAxruAL scii:nx'Es of Philadelphia. 91 



descriptions and figures, when sucli exist, have been used in the behef 

 that they are more Ukely to be accurate. The literature list is as 

 accurate and complete as lay in the writer's ])ower to make it, l)ut it 

 has been found wellnigh impossible to collect all of the scattered refer- 

 ences to the genus. If either the table of species or the literature list 

 j-jroves helpful to an}' student of the group, or serves to faciliate com- 

 parison of the characters of the various species, it will have fulfilled its 

 purpose. The characterization of the genus has been added for the 

 sake of completeness. 



Genus DINOPHILUS. 



Minute wormlike forms, generally displaying an external division 

 into segments, delimited bj' constrictions; each trunk segment, includ- 

 ing the head, bearing one or two bands or circlets of long cilia; in addi- 

 tion to these a ciliated strip clothes the ventral surface. The last seg- 

 ment bears a conical caudal appendage. The anterior surface of the 

 head usually provided with sense hairs. Alimentary canal well 

 developed (except in the degenerate males of certain species), consist- 

 ing of a mouth opening on the ventral surface of the head ; an oesophagus 

 provided on its posterior inner surface, where it joins the mouth, wdth 

 an eversible proboscis; a capacious stomach, and a short intestine ter- 

 minating dorsad to the caudal appendage. Coelom represented by the 

 cavities of the gonads. A primary body cavity of varying extent 

 always present. Nervous system consisting of a simple brain, a pair 

 of circumoesophageal commissures, and, continuous with the latter, tw^o 

 ventral cords, embedded in the hypodermis. In some members of the 

 group, at least, are also present transverse commissures and pairs of 

 ganglia correlated with the segments as indicated on the exterior. 

 Nephridia, when present, of the protonephridial or larval type, and 

 arranged metamericall}^ 



Table of Species of Dinophilus. — 



A. — Sexes monomorphic. 



B. — Gonads paired, extending to the anterior extremity of the 

 trunk. Two bands of cilia borne b}- each trunk 

 segment. 

 C. — ^Trunk segments 6. 



D, — Caudal appendage 3-segmented vorticoides. 



DD. — Caudal appendage unsegmented, ... gardineri. 



CC. — Trunk segments 5, tceniatus. 



BB. — Gonads Y-shaped; only one Ijand of cilia borne on each 

 trunk segment, gigas. 



