56 MESOZOIC AND CENOZOIC ECHINODEKMATA OF THE UNITED STATES. 



PSEUDODIADEMA DIATEETUM (Morton). 



Plate XIX, figures la-f . 



Cidaris diatretum Morton, 1833, Am. Jour. Sci., lstser., vol. 23, p. 294. 

 Cidarites diatretum Morton, 1834, Synopsis Organic Remains Cretaceous, p. 75, PI. X, fig. 10. 

 Cidaris diatretum Bronn, 1S48, Index palseontologicus, vol. 1, p. 298. 

 Pseudodiadema diatretum Desor, 1858, Synopsis des 6chinides fossiles, p. 73. 

 Cidaris diatretum Gabb, 1859, Cat. Invert. Fossils Cretaceous, p. 18. 

 Pseudodiadema diatretum Cotteau, 1862-1867, Paleontologie francaise, vol. 7, p. 519. 

 Pseudodiadema diatretum Meek, 1864, Smithsonian Misc. Coll., vol. 7 (177), p. 2. 

 Pseudodiadema diatretum Conrad, 1S68, Geology of New Jersey, appendix, p. 722. 

 Cidaris clavigera Credner, 1870, Deutsche geol. Gesell. Zeitschr., vol. 22, p. 218. 

 Cidaris sceptrifera Credner, 1870, Deutsche geol. Gesell. Zeitschr., vol. 22, p. 218. 

 Pseudodiadema diatretum Clark, 1891, Johns Hopkins Univ. Circ, vol. 10, No. 87, p. 75. 

 Pseudodiadema diatretum Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 51. 

 Pseudodiadema diatretum Clark, 1893, U. S. Geol. Survey Bull. 97, pp. 46, 47, PI. XIII, figs. la-f. 

 Pseudodiadema diatretum Johnson, 1905, Acad. Nat. Sci. Philadelphia Proc, vol. 57, p. 6. 



Pseudodiadema diatretum Weller, 1907, Cretaceous paleontology of New Jersey: Geol. Survey New Jersey, pp. 285-286 r 

 PL IX, figs. 1-6. 



Determinative characters. — -Test circular, convex below, sides inflated. Ambulacra wide, 

 sinuous, with two rows of tubercles that are large at the ambitus and decrease toward the poles; 

 primary tubercles and several irregular rows of secondary tubercles. Peristome narrow, about 

 one-third the diameter of the test. 



Dimensions. — Diameter 30 to 37 millimeters; height 12.5 to 15 millimeters. 



Description. — The specimens vary greatly in size,' the full-grown forms being moderately 

 large. The sides are inflated. 



The ambulacra are wide, slightly raised, and furnished with two rows of tubercles, thirteen 

 to fourteen in each row. They are large and prominent at the ambitus but decrease gradually 

 toward the poles. The broad areolas, that are sharply depressed in their marginal portions, are 

 striated by faint radial ridges on the outer parts. At the upper and inner angle of each plate is 

 a small secondary tubercle, while irregularly scattered over the other portions of the plates are 

 smaller tubercles, and between them minute granules. The poriferous zones are slightly flexed, 

 the pores of each plate being disposed in curved form about the margin. Although' there are 

 generally three pairs of pores at each plate, four pairs are not infrequent near the ambitus. 



The interambulacra are about one and one-half times the width of the ambulacra, and have 

 two rows of tubercles somewhat larger than those of the latter. There are, in addition, several 

 irregular rows of secondary tubercles, of various sizes, that are most numerous between the rows 

 of primary tubercles and the poriferous zones. Sparsely scattered over the interambulacral 

 space are flattened granules. 



The primary tubercles of both the ambulacra and interambulacra have wide circular areolas, 

 elevated and deeply crenulated bosses, and distinctly perforated mamelons. 



The peristome is narrow, reaching scarcely one-third the diameter of the test. The incisions 

 of the margin are weak. 



The discal opening is subpentagonal. 



Related forms. — This species resembles in some particulars Pseudodiadema ornatum Goldfuss 

 of the Cretaceous of Europe, but the latter form has a different arrangement of the secondary 

 tubercles and granules and lacks the radial striation upon the areolas. 



Localities. — Gloucester (type), Timber Creek, and Vincentown, N. J. 



Geologic Ttorizon. — Vincentown sand of Rancocas group, Upper Cretaceous. 



Collections. — Academy of Natural Sciences of Philadelphia (1471); New Jersey Geological 

 Survey; American Museum of Natural History, New York. 



Genus HETERODIADEMA Cotteau. 



Heteeodiadema oenatum Clark, n. sp. 



Plate XVIII, figures 2a-f. 



Determinative characters. — Test small, subcorneal, ambitus tumid, aboral surface depressed, 



lower surface convex; apical opening large; ambulacral plates with two vertical rows of small 



