PACIFIC COAST OLIGOCH MTA. 
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PONTODRILUS Grube. 
The genus Pontodrilus, together with Photodrilus, is distinguished from all re- 
lated genera by the absence of nephridia in the twelve anterior somites. In the 
majority of species the nephridia commence in somite xiii, but in two species they 
commence respectively in xiv and xv. A common character to all the species appears 
to be the very great thickening of the septa between somite v and xiii. 
I have so far on the Pacific Coast only found one species of the genus Ponto- 
drilus. Examinations were made from alcoholic specimens, I having no opportunity 
to examine them when [ found them in their native habitat—Mexico. 
Pontodrilus Michaelseni n. sp. 
This species differs from all other species, except P. Maronis,* which have been 
referred to this genus in possessing a glandular crop occupying somites xiv, xv and 
xvi, as well as in other minor details. The habitat of the species is the very narrow 
moist line between high tide and dry soil on the shores of the Gulf of California 
around Guaymas, Mexico. The soil in which it occurs is very sandy and thoroughly 
soaked or moistened with the strongly saline water of the gulf. It occurred here in 
large numbers, but unfortunately at my visit most of the specimens were immature, 
only two possessing clitellum in the end of November, 1895. I dedicate this species 
to Dr. W. Michaelsen of Hamburg, whose labors in our common field are among the 
the most thorough and best. 
EXTERIOR CHARACTERS. 
The body of this species reaches a length‘of 3} inches with a width at the 
clitellum of less than } of an inch, but the majority of specimens are somewhat 
smaller. The above measurement refers to specimens slowly killed and then hard- 
ened in alcohol. The body is tapering towards the tail end, the latter however being 
slightly swollen (fig. 24). 
The prostomium encroaches on somite i, dividing it about one-half. Somite i 
is slightly larger than any of the following somites (fig. 25). 
The clitellum commences in xiii and in full-grown specimens includes part of 
xix. It is incomplete in a peculiar manner. In xiii to xvii inclusive it is only 
developed on the dorsal side of the body. But in xviii and in part of xix the clitellum 
is only developed on the ventral side of the body, though this fact cannot be ascer- 
tained from exterior inspection. Viewed from the underside the clitellum appears to 
be on a line drawn through seta one. Between xvii and xviii the clitellar swelling 
recedes slightly, again to widen out in xviii, and here joining to a pair of ventral 
cushions, between which and the clitellum proper are situated the male pores. 
Another pair of swellings are noticed around the spermathecal pores, covering 
“I received M. Perrier’s memoir on Pontodrilus only after this paper was partly in print. 
