BRACHIOPODA. 3b7 
Dinobolus (?) parvus.] 
Shell substance originally not very thick, apparently smooth and now replaced 
by a coarsely crystallized calcite, a feature common to many species of the Trimer- 
ellide, 
Of this species we have but a single specimen from Minnesota, found by Mr, E. 
O. Ulrich, which is in an excellent state of preservation. The interior characters 
are shown in greater detail than appears to have been the case in the material from 
Wisconsin upon which Prof. Whitfield based the species, otherwise the example 
agrees with his description and illustrations. In size and form it is nearer to 
Dinobolus schmidti Davidson and King,* from the Lyckholmer Schicht at Kirna, 
Esthonia, a horizon nearly equivalent to the Trenton limestone of New York, 
than to Obolellina canadensis and O. magnificus Billings** from the Black River group 
of Canada. The latter, of which only the exterior is known, are also much larger 
species than D.? parvus. 
The interior of D.? parvus, as revealed in the Minnesota specimen, is highly 
instructive, since it appears to have characters both of the Obolidw and Trimerellide. 
The structure of the cardinal region is similar to that of Obolel/a, while the platform 
and its muscular scars are as in Dinobolus. The crescent so characteristic of Din- 
obolus is, however, absent in D. parvus. The diverging elevations on each side of 
the pedicle muscle sear in Obolella crassa, (the cardinal scars), are also present in 
D.? parvus and occupy a position equivalent to the crescent of Dinobolus. It may 
be that here is indicated the line of development of the crescent from the cardinal 
sear of Obolelia. The combination of these characters in D.? parvus seems to require 
its separation from Dinobolus, but until the interior is known of the species referred 
by Billings to Obolellina it is better to leave it provisionally in the former genus. 
Lower Silurian species of Dinobolus are also known from Esthonia (D. schmidti) and 
Brittany (D. brimonti Rouault+), but these have well-developed crescents. 
Formation and locality —Middle Galena, Wykoff. 
Collector.—B. O. Ulrich. Type in the collection of C. Schuchert. 
*Quart. Jour. Geol. Soe. London, vol. xxx, p. 164, pl. xix, figs. 5, 6, IS74, 
**Canad. Nat. Geol. vol. iii, p. 441. 1858; vol. vi, n. ser., p. 329, 1872. 
+See Davidson’s paper in the Geol. Mag,, vol. vii, decade ii, p. 340, 1880. 
