194 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



The following description will be confined to the points 

 of difference between the species and subspecies. A closer 

 comparison can only be made through a study of type 

 specimens of the species. 



External Characters. 



Color. — The whole worm is semi-transparent, of a delicate 

 flesh-color, with blood-vessels appearing through the skin. 

 The spermathecse and prostates appear as white masses 

 through the skin. 



Somites. — The somites are all faintly three-ringed. The 

 clitellar somites XIII-^ XVIII are much more distinct and 

 wider than the somites posterior to them. According to the 

 figure given by Ude the clitellar somites of D. singularis 

 are of about the same width as the somites posterior to them. 

 The clitellum ends posteriorly and dorsally with the centre 

 of XVIII, but ventrally with the posterior margin of XVII. 

 In D. singularis the clitellum appears to extend to the 

 posterior part of XVIII, while ventrally it does not cover 

 the whole of XVII. 



The prostomium (fig. 137) divides somite I by almost 

 two-thirds. It is bounded posteriorly by a deep transverse 

 groove which extends across the whole somite in the direc- 

 tion of the short diameter of the body. 



The dorsal -pores begin in IX. The pores increase 

 gradually in size posteriorly, those immediately in front of 

 the clitellum are larger. The pores in the clitellar somites 

 are also distinct. The most anterior pore is situated on the 

 anterior part of IX. In several somites anterior to the first 

 dorsal pore there are deep depressions which appear, when 

 viewed from the surface, as narrow pores. Longitudinal 

 sections show that these depressions do not penetrate the 

 body-wall. Undoubtedly such depressions have sometimes 

 been mistaken for true pores. 



Genital Zone. — (fig. 137B.) There are two slightly 

 curved grooves with the convexity towards the median line. 

 They are slightly wavy and surrounded by a slight 



