148 MESOZOIC AND CENOZOIC ECHINODEKMATA OF THE UNITED STATES. 



Genus BREYNELLA Gregory. 

 Breynella gregoeyi Twitchell, n. sp. 

 Plate LXVIII, figures la-f. 

 Breynella sp. Gregory, 1891, Geol. Soc. America Bull., vol. 3, p. 104. Nornen nudum. 



Determinative characters. — Test suboval in marginal outline, broadest back of the center, 

 narrowing posteriorly, truncated vertically at the posterior end; sides and anterior end rounded; 

 upper surface convex, somewhat elevated, especially along the posterior median area, apex 

 slightly to the rear of the center; under surface rather flat, slightly concave near the peristome. 

 Ambulacra! areas narrow, supetaloid; petals rather short, straight, flush, inconspicuous and 

 open at the ends. Apical system very excentric anteriorly. Peristome pentagonal, excentric 

 anteriorly, but somewhat less so than the apical system; with a floscelle. Periproct oblong-oval, 

 longitudinally elongate, supramarginal, at the top of, and flush with the vertical surface of the 

 posterior truncation. 



Dimension. — Length 34 millimeters; width 28 millimeters; height 18 millimeters. 



Description. — This medium-sized Breynella is the first representative of the genus to be 

 reported from the United States. The specimens here described are probably the same which 

 J. W. Gregory saw at the American Museum of Natural History, and as he first recognized the 

 form as a Breynella it is named in his honor. The test of this species is suboval to subovate 

 in marginal outline, broadest back of the center, narrowing toward the posterior end, which 

 is vertically truncated. The sides are rounded and inflated; the upper surface convex, some- 

 what elevated, especially along the posterior median area, which, however, gradually declines in 

 the form of a low rounded ridge on approaching the region of the periproct; the under sur- 

 face rather flat, tumid around the margin, slightly concave near the peristome. The apex is 

 slightly to the rear of the center. 



The ambulacral areas narrow, widest at the ambitus, where they are only slightly wider 

 than the petaloid portions; dorsal portions subpetaloid, the petals being rather short, straight, 

 flush, inconspicuous, and open at the ends; the posterior pair slightly longer than the others, 

 which are nearly equal in length. The poriferous zones are rather narrow; outer row of pores 

 oval, inner row round; pairs of pores conjugate. 



The apical system is very excentric anteriorly, being situated about one-third the length 

 of the test from the anterior end. Its details are not well shown on the specimens studied; but 

 there are four genital pores of which the anterior pair are nearer together than the posterior. 



The peristome is pentagonal, transversely elongate, excentric anteriorly, but somewhat less 

 so than the apical system, with a floscelle. The floscelle is distinct, and the bourrelets are broad 

 and rather prominent; but the phyllodes are not very conspicuous. 



The periproct is oblong-oval, longitudinally elongate, supramarginal, at the top of, and 

 nearly flush with the vertical surface of the posterior truncation. A poorly defined shallow 

 groove extends from the periproct down the middle of the posterior truncation. 



The surface of the test is closely set with small tubercles, in deep scrobicules, which are 

 somewhat larger on the under surface. There appears to be a very narrow, somewhat pitted, 

 median band behind the peristome which extends along close to the zigzag suture line. 



Related forms. — Breynella gregoryi resembles in a general way several of the Tertiary species 

 of Cassidulus; but is readily separated by its longitudinally elongate periproct. Its closest 

 American ally is Ecliinantlius antillarum Cotteau, from the Eocene of the West Indies, from which 

 it differs in having its periproct overhung by an expansion of the test. It resembles E. lonissenti 

 Cotteau, from the Eocene of France, but is smaller and has its apical system more excentric 

 anteriorly. It also closely resembles Breynella eqiiizoata Gregory, from the lower Oligocene of 

 Malta, but may be distinguished by its higher posterior margin and the slightly more anteriorly 

 excentric position of both its apical system and peristome. 



Locality. — Santee Canal, S. C. 



Geologic horizon. — Probably either the Cooper marl (upper Eocene) or the upper part of 

 the McBean formation (middle Eocene) . 



Collection. — American Museum of Natural History. 



