136 
* PALAEONTOLOGY OF NEW YORK. 
narrow elliptical slit, which extends scarcely for one-half the face of the cone, 
thence merging into the inner sipho. The surface of the shell is covered with 
simple, elevated, concentric lines of growth which are interrupted by the slit. 
The ventral [= brachial] valve is very depressed-convex or even flat; its beak 
is sharply defined, depressed, directed toward the cardinal margin, and in no 
sense marginal, for between it and the margin are several unbroken growth¬ 
lines.” 
Further, under the discussion of the type-species, S. elliptica, Kutorga, the 
author observes (p. 274): 
“ The study of the slit under the microscope, with an aplanative ocular and 
enlargement of 45 diameters, convinces me that there is no fissure in the bot¬ 
tom of the slit opening into the interior of the shell. It is very clearly seen 
that the bottom is .covered with the same epidermal layer crossed by fine 
growth-lines; and, further, that the posterior end of the outer slit merges into 
the cylindrical sipho.” 
It is important to have these latter observations in mind, for while they agree 
minutely with the character of the aperture in Orbiculoidea, Davidson, the feature 
is not so well understood from a study of Kutorga’ s figures. It thus appears 
that there is no essential difference in Schizotreta, Kutorga, and Orbiculoidea, 
Davidson, and the former term may very well stand to include those forms 
essentially in agreement with Orbiculoidea, D’Orbigny, but having thicker 
shells and the relative convexity of the valves reversed, bearing, in fine, the 
same relation to D’Orbigny’ s genus as Strophonella to Strophodonta, among 
the articulate brachiopods. 
Professor Dwight has shown that the muscular impressions of the brachial 
or imperforate valve- in Schizotreta conica, consist of two strong excavated ante¬ 
rior adductors approaching toward the center of the shell, and separated by a 
prominent septum which is continued from a somewhat thickened posterior 
muscular area. Better preserved interiors of this species will, no doubt, show 
other scars and determine more closely its relations in these respects to Orbicu¬ 
loidea nitida and Discinisca lamellosa. 
Another peculiar phase of reversion in certain features characterizing the 
typical Orbiculoidea, is seen in the species Discina grandis, Vanuxem, a not 
