OLIGOCEXE ECHINODERMATA. 169 



Localities. — Richards Quarry, Ocala, Marion Comity, and Johnsons Lime Sink, Levy 

 County, Fla. ; Flint River near Bainbridge, Baker County, Ga. Conrad's specimen came from 

 a well near Bainbridge, Ga. 



Geologic horizon. — Vicksburg group, lower Oligocene. The specimens from Ocala are from 

 the Ocala limestone. 



Collections. — U. S. National Museum (112506, A; 164661, B) ; Wagner Free Institute of 

 Science. 



Oligopygus flokidanus Twitchell, n. sp. 



Plate LXXIX, figures la-f. 



Determinative characters. — Test with thick walls, oval, narrowing anteriorly; sides tumid; 

 upper surface convex, elevated anteriorly, slightly depressed posteriorly; under surface with a 

 deep, relatively short and narrow transverse depression around the peristome. Ambulacral 

 areas wide at the ambitus, from which they gradually narrow to the peristome and apex; dorsal 

 portions subpetaloid; petals wide open. Apex excentric anteriorly; apical system central or 

 slightly excentric anteriorly. Peristome pentagonal, opening at the bottom of the depression 

 in the under surface. Periproct very small, circular, situated about midway between the peri- 

 stome and posterior margin. 



Dimensions.— Length 37 millimeters; width 31 millimeters; height 19 millimeters. The 

 dimensions of another specimen were, length 48 millimeters; width 42 millimeters; height 26 

 millimeters. 



Description. — This new species of Oligopygus is rather rare, only three specimens being 

 known to the writer. De Loriol may have possessed a specimen, for some of the characters he 

 ascribes to 0. wetherbyi apply more correctly to this species. The test is usually thick, especially 

 at the ends; oval on marginal outline, though somewhat narrower toward the anterior end; 

 margin rounded and inflated, the anterior end more so than the posterior, giving that end a 

 bulging appearance in a forward direction. The upper surface is convex, somewhat elevated 

 forward of the center, declining gradually toward the posterior end and sloping somewhat 

 steeply on the sides; under surface tumid but slightly concave transversely near the middle, 

 with a deep transverse depression around the peristome. The apex is forward of the center. 



The ambulacral areas are wide at the ambitus, from which they gradually narrow to the 

 peristome and apex, there being hardly any constriction at the ends of the petaloid portions, 

 the anterior paired ambulacra curving posteriorly on approaching the peristomial depression; 

 dorsal portions subpetaloid, the odd petal being somewhat longer than the posterior pair, which 

 are somewhat longer than the anterior pair. The poriferous zones are narrow, nearly straight, 

 and gradually diverge from their origin at the apex to their extremities, which are wide apart; 

 pores small, oval, equal and conjugate. There are also several pairs of very small pores near 

 the outer end of each plate from the ends of the petals to beyond the ambitus The interporif- 

 erous areas are slightly tumid, standing out in relief in the unweathered specimen, so as to form 

 five straight radial ridges from apex to ambitus. 



The apical system is central or somewhat excentric anteriorly. The madreporite is large 

 and tumid, central, shield shaped; the posterior end being pointed and extending between the 

 posterior radial plates. There are four genital pores, situated at the edge of the madreporite, the 

 posterior pair being farther apart than the anterior; and there are five small radial plates, each 

 perforated by a very small pore. 



The peristome is pentagonal and opens at the bottom of a deep, transverse depression in 

 the middle of the under surface. This depression is relatively short and narrow; its length at the 

 surface being about one- third the width and its depth about one-thud the height of the test. Its 

 anterior wall is nearly vertical or even inclined slightly toward the anterior end but at a much 

 steeper angle than the posterior wall, thus forming a deep, narrow, anteriorly projecting 

 concavity. 



The periproct is very small and circular; and situated about midway between the peristome 

 and the posterior margin. 



