172 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



regarded as different species were it not for the intermediate forms found in the large amount 

 of available material. Many of the specimens are only well-preserved casts. 



The test is irregularly subcorneal in form; the marginal outline broadly ovate, broadest 

 back of the middle; margin thick and vertically flattened along the anteriorly converging side 

 portions, more or less angular at the ends, sharply angular beneath the periproct. The upper 

 surf ace varies from rather low and depressed to moderately high. It is irregularly subcorneal; 

 the apex being more or less excentric anteriorly, the side and anterior surfaces sloping nearly 

 equally and somewhat steeply though with a more or less rounded contour, and the posterior 

 surface sloping less steeply and being more or less flattened, except for a slight tumidity above 

 the periproct. The under surface is concave along the longitudinal median area. The apex is 

 excentric anteriorly, sometimes coincident with, sometimes anterior to the apical system. 



The ambulacral areas are narrow at the ambitus, dorsal portions petaloid; petals rather 

 wide, long, the posterior pair slightly longer than the anterior pair which are slightly longer than 

 the odd petal, rather sharply pointed at both ends, almost closing at their extremities. The 

 poriferous zones are rather wide, slightly depressed; pores subequal, outer row oval, inner row 

 round; pairs of pores conjugate; interporiferous areas slightly tumid. 



The surface of the test is closely set with small scrobiculate tubercles which increase in size 

 on the under surface except along a rather narrow pitted median area. 



The apical system is excentric anteriorly in most specimens, but is subcentral in some. In 

 most it is coincident with the apex but in some it is slightly back of it. Because of the poor 

 character of the specimens, the details can rarely be made out. There are four perforated basal 

 plates, the anterior genital pores being nearer together than the posterior, and five small perfo- 

 rated radial plates. 



The peristome is pentagonal, somewhat elongate transversely, excentric anteriorly, more so 

 than the apical system, being about three-eighths the length of the test from the anterior margin; 

 and apparently more fixed in its relative position than the apical system. It is surrounded by a 

 well-defined floscelle with rather prominent bourrelets. On the casts the phyllodes form prom- 

 inent radial ridges around the peristome. 



The periproct is moderately large, elliptical, transverse, supramarginal, rather low and near 

 the posterior end, beneath a low, rounded, transverse expansion of the test. Beneath the peri- 

 proct there is a depression which renders the margin at this point thinner or more sharply angular 

 than it is elsewhere. 



Related forms. — -Among American forms Cassidulus gouldii is most nearly related to 0. ala- 

 hamensis but can readily be distinguished by its smaller size, less subquadrate form, and more 

 steeply sloping sides. It does not appear to very closely resemble any foreign forms. 



Localities. — Baker County (type); Laurenden Creek; Hawkinsville ; A. E. Belcher's well, 

 Decatur County; 32 mdes south of Macon, on Georgia & Florida Railroad; Ellaville; 2h miles 

 north of Cuthbert, Ga. Two miles south of Gainesville; 6 miles southwest of Lake City; Santa 

 Fe River, Alachua County, Pembertons Ferry, Withlacoochee River 4 and 5 miles west of Live 

 Oak; deep wells at Padlock, 7 miles south of Live Oak; Sulphur Springs Ferry, Suwannee 

 County, Fla. 



Geologic horizon. — Vicksburg group, lower Oligocene, possibly Eocene also. Bouve said 

 his form was from the "Millstone grit" and Conrad said his was from the "Buhrstone"; con- 

 sequently the species has hitherto been regarded as Eocene ; but nearly all of the large number of 

 specimens studied by the writer came from Oligocene deposits. 



Collections. — Boston Society of Natural History (1756, A); U. S. National Museum (137904, 

 B; 137904a, C); Academy of Natural Sciences of Philadelphia; Wagner Free Institute of 

 Science. 



Cassidulus (Pygorhynchus) alabamensis Twitched, n. sp. 



Plate LXXX, figures 3a-d. 



Determinative characters. — Test large, subquadrate, depressed; upper surface convex, 

 declining from apex nearly equally on all sides; under surface concave longitudinally. Apex 

 subcentral, slightly to the rear of the anteriorly eccentric apical system. Ambulacral areas 



