230 Fossil Annelids from the Lower Silurian. 
less furnish data for a more extended description, with numer- 
ous illustrations, which it is hoped will soon be completed. 
Nereidavus varians, gen. et sp. nov. 
The jaw selected as a type for the genus (fig. 1), is one of the 
largest and most perfectly preserved of those at hand. It is 
ark brown, with a coppery luster in some places, this coloring 
being due to the weathered condition of the specimen. It is 
hollow at the base and throughout the greater part of its length, 
and so strikingly resembles the jaw of the common Nereis pela- 
gica Linn. of the Atlantic coast, as to render their near affinity 
almost certain. The denticulations, or teeth, are eight in num- 
ber, but were probably more numerous originally, since the pos- 
terior portion of the specimen is wanting. The anterior tooth, 
which is the largest, is somewhat twisted outward, not Iving 10 
the same plane with its fellows. The length of the specimen 1s _ 
5°6 mm., the depth beneath the fourth tooth 1-4 mm. 
A second very perfect specimen, which may possibly belong 
with the jaw above referred to, is represented in fig. 2. It con- 
tains eighteen teeth, the anterior one quite long and stout, the 
next five mere slight protuberances, and only to be seen under 
the microscope, while the remaining teeth are sharp and strong. 
The length of the exposed portion of this individual is 2°8 
mm.; depth under the first of the strong teeth, the seventh in 
the series, 22 mm. Since the base of this specimen is burie 
in the rock and cannot be seen, it is not altogether certain 
what it is. It bears some resemblance to one of the seta of 
Nereis Dumerihi, Aud. and M. Ed., figured by Ehlers in his 
work entitled Die Borstenwiirmer, pl. XX, fig. 31. 
e specimens under consideration were collected by Profes- 
sor A. G. Wetherby, near Cincinnati, Ohio. Through the en- 
ergy and courtesy of this naturalist, a large suite of specimens 
has been secured and forwarded to New Haven, and to bim 
the writer would express his grateful acknowledgments. 
Yale College Museum, New Haven, Conn., July 28th, 1877. 
