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



beyond somite I, Beddard (86) has nevertheless found it 

 necessary to question the presence of this lobe. Thus we 

 find in his definition of the species, " prostomium absent." 

 My sections show conclusively that Horst is correct in 

 his statement, and that a prostomium is really present, 

 though it is of small size (supposing, of course, that my 

 Mexican specimens do not differ in character from those 

 of Horst, or that Beddard and Horst really examined the 

 same species, of which I am not convinced). 



The prostomium is frequently retracted, and in specimens 

 which have been directly immersed in alcohol it is probably 

 always retracted to such an extent that it cannot be seen 

 from the exterior. In figs. 2 and 3 the prostomium is shown 

 as seen from the lateral and ventral sides ; in fig. 4 it is 

 seen retracted. This peculiarity probably accounts for the 

 statements of various authors as to its presence or absence. 



The inner, anterior lips (fig. 9) of the prostomium are 

 distinct and swollen, showing a bilobed apex. The entrance 

 to the alimentary canal begins between the two lobes. 



Somite I is much wider dorsally than ventrally, as shown 

 in fig. 9. The surface of the posterior part of somite I is 

 sulcate in the direction of the long diameter of the body, 

 and the whole of somite H is similarly sulcate and rugose 

 (figs. 2-4). Somite II is much wider than somite III and 

 slightly wider than the dorsal part of somite I. Somite II is 

 the most anterior somite having set^. The anterior somites 

 increase in width towards IX, and somites VI-IX are gen- 

 erally much shorter and more prominently ringed than the 

 others. Somites X to XIV are of almost the same size, and 

 the middle ring of each of these somites projects much less 

 than do those in the anterior somites. 



Clitelluni. — (fig. 5.) The clitellum begins with somite 

 XV and extends through one-fourth of XXII. It is well 

 defined, especially with the beginning of the anterior part 

 of somite XV. Anterior to this, the body is narrower than 

 in somite XV and those following. 



Exteriorly viewed, the clitellum is saddle-shaped, but 

 there is a continuous row of clitellar cells even on the 



