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 suriiiee 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 



