GASTROPODA. 847 
Protowarthilda.] 
Microceras, Hall, 1845. (Amer. Jour. Sci., vol. xlviii, p. 249.) Minute shells 
(1 to 4 mm. in diameter), gregarious in habit, in form like Cyrtolites. It is difficult 
to decide whether any of hundreds of specimens seen preserve the shell or not, 
though we are inclined to regard them as casts of the interior. They are always 
of a black or brownish color, with the surface perfectly smooth and generally 
glossy. The principal and typical species, M. inornatus Hall, seems to range from 
the Trenton to the Devonian. 
The shells comprised in this somewhat doubtful genus are certainly not “embry- 
onic volutions of bellerophontes,” as supposed by Waagen, but they may be dwarfed 
varieties of species of Cyrtolites and perhaps of other genera. They usually occur 
associated with large numbers of Cyclora, another genus of minute gastropods, the 
species of which again may be but dwarfed forms of Holopea or Cyclonema and 
Lophospira, and with very small species of Ctenodonta and Clidophorus, 
Cyrtonitrina, n. gen. (Ulrich.) (Cyrtolites [part.], Lindstrém, 1884.) Symmetri- 
cally involute, small thin shells, consisting of one and a half or two rapidly 
enlarging, contiguous or free volutions, with rounded sides and a more or less well 
developed slit-band; aperture higher than wide, sinuate dorsally and somewhat 
deeply emarginated in front of the slit-band; marks of growth curving strongly 
backward, more or less distinctly lamellose, with crenulated edges and, when 
distant enough, traversed by small wrinkled longitudinal riblets. Type, Crytolites 
lamellifer Lindstrém. In the same work (Silurian Gastropoda of Gotland, pp. 82-84) 
Lindstrém describes three more species belonging to this genus, viz.: Crytolites 
pharetra, C. arrosus and C. obliquus. In America the new genus is represented by 
Crytolites nitidulus Ulrich (Jour. Cin. Soc. Nat. Hist., vol. ii, p. 12; 1879), a species of 
the upper part of the Trenton group. 
Family PROTOWARTHIDA 
Symmetric, involute shells; aperture not abruptly expanded; outer lip and 
lines of growth with a broad or narrow dorsal sinus; slit and band wanting. 
OWENELLA, n. gen.* Shell thin, subglobose, closely coiled; volutions compressed 
dorso-ventrally, moderately embracing, rounded on the back, enlarging gradually, 
not abruptly expanded at the aperture; umbilicus open; aperture transverse, the 
outer lip with a rather broad and not very deep median insinuation; slit-band wanting. 
So far as known the surface markings consist of transverse or growth lines only. 
Type, Bellerophon antiquatus Whitfield, Upper Cambrian, Wisconsin. B. pettos 
Koken, from Lower Silurian strata in Hurope, seems to have all the essential char- 
acters of this genus. 
* Named for that great pioneer in the geology of the northwestern states, Dr. David Dale Ow en. 
