624 THE PALEONTOLOGY OF MINNESOTA. 
[Sphenolium parallelum. 
have evidence to show that this disproportionate development of the posterior end 
was a gradual process, an undescribed species from the Utica horizon at Cincinnati 
being intermediate in this respect between the Trenton forms and those occurring 
in the middle and upper beds of the Cincinnati group. 
SPHENOLIUM PARALLELUM, 7%. Sp. 
PLATE XXXVI, FIGS, 42 and 48. 
Shell elongate subovate, rather strongly convex, the thickness, hight and length 
respectively as one is to one and two and one-fourth. Dorsal margin straight, nearly - 
parallel with the ventral, terminating posteriorly in an obtuse angle where it joins 
the obliquely rounded posterior margin; anterior end short, apparently narrowly 
rounded; basal line very gently convex; posterior end rather abruptly rounded in 
the lower half. Beaks prominent, full, incurved; umbonal ridge strongly convex, 
somewhat emphasized by a slight furrow immediately above it in the cardinal slope; 
another obscure furrow borders the dorsal edge. A small but well marked lunule 
in front of the beaks, and a narrow and rather illy defined channel behind them. 
Central and anterior parts of valves rather strongly convex. Surface marked con- 
centrically with very fine striz and afew more or less obscure undulations. The 
latter are more distinct and regular on the umbonal ridge than elsewhere. 
The subparallel margins distinguish this species from the more typical forms of 
the species described by Miller from the Cincinnati rocks. 
Formation and locality.—‘ Lower Blue” beds of the Trenton formation, Mineral Point, Wisconsin. 
Mus. Reg. No. 8346. 
SPHENOLIUM STRIATUM, , Sp. 
PLATE XXXVI, FIGS. 44 and 45. 
The shape and general expression of this shell is almost exactly the same as in 
the preceding, S. parallelum, yet when critically compared certain differences are 
observed which render a separation necessary. The specimens are not very perfect 
casts of the interior and exterior, still they preserve traces of very fine radiating 
lines on the umbonal ridge and a few coarser ones on the cardinal slope which, if 
such had been present on S. parallelwm, would undoubtedly show on the excellently 
preserved cast upon which that species is founded. The Galena specimens again 
present a number of small, regular and short concentric folds on the anterior end, 
but they are wanting on the sides and posterior end where the folds are rather 
distinct in the Lower Trenton species. In comparing the outlines a slight difference 
is to be detected in the postero-cardinal region where, instead of being subangular 
