ANATOMICAL STRUCTURE OF KERRIA. 295 



are present. The posterior nephridia are thickly covered 

 with peritoneal cells, and are very large, filling the somite. 



Habitat. In mud at Miraflores near San Jose del 

 Cabo, Cape Region of Baja, California. Species named 

 in compliment to James M. McDonald of San Francisco. 



The body offers little that is characteristic. In out- 

 ward form it resembles more Gordiodrilus than Ocnero- 

 drilus, judging from the figures given by Beddard, 

 though there can be but little outward difference between 

 the two genera. The prostomium and peristomium are 

 quite large, wider than any of the following three somites 

 (ii to iv), which are quite narrow. Somites v to ix are 

 much wider, and somites v, vi and vii are also much 

 higher than any of the others, those of the clitellum 

 not excepted. From somite viii the body narrows gradu- 

 ally down to the clitellum which is only slightly wider 

 and not equal in width to the thicker anterior part of the 

 body, occupied by somites vi to viii. 



The clitellitm covers somites xiii to xx and is developed 

 only superiorly and laterally, just as in Ocnerodrilus. 

 The posterior part of the body tapers gradually towards the 

 tail end which is narrower thanin Ocnerodrilus. In alco- 

 holic specimens the body is always strongly bent at somites 

 X and xi, the clitellum being often included in the bend. 

 This bend makes longitudinal sectioning difficult, or 

 at least unsatisfactory, the genital papillse being always 

 folded or distorted, the more so as the bend is al- 

 ways toward the ventral zone. All Ocnerodrilid^e bend 

 when placed in alcohol, but none to the same extent as 

 this Kerria. The body-wall of the anterior somites 

 is thicker than in Ocnerodrilus. This is especially the 

 case with the ventral region of somites iitoix; the dorsal 

 region of these somites is also thick but less so than the 

 ventral one. Somites x, xi and xii are very thin walled 



