6 PROCEEDIN-GS OF THE NATIONAL MUSEUM vol. 72 



* 'The ambulacral areas between the pore bands are distinctly ele- 

 vated. The ambulacral plates in the petals are long horizontally and 

 very narrow, and consequently very numerous. The interambulacral 

 plates are much larger, the largest ones being three or four times- 

 as long horizontally as they are wide. The whole upper surface is 

 densely packed with tiny primary and secondary tubercles ; even the 

 ridges between the pore slits support each a row of tubercles; each 

 primary is surrounded by a distinct areola and on some of the 

 primaries a minute mamelon can be detected. The base is covered 

 with similar larger and more widely spaced primary tubercles with 

 distinct mamelons, some of which can be seen to be perforated, and 

 each primary is surrounded by a relatively broad areola; the 

 secondaries are tiny and relatively few. 



The apical system is situated 0.46 the length of the test from the 

 anterior end; as seen in a slightly worn specimen, the madreporite 

 is subcircular and relatively very large, the three other genital 

 plates are small and perforated, and the ocular plates are minutey 

 with no sign of perforations; as seen in a more deeply worn 

 specimen, the madreporite is relatively smaller, the other genitals 

 are larger, the oculars are larger and perforated. The raised apical 

 sj'^stem on the specimen shown in Plate 3, Figures 1, 2, is apparently 

 an abnormal feature, as none of the other specimens possess it. The 

 significance of this peculiar feature is not known, but Austin H. 

 Clark has called my attention to a similar raised apical system on 

 one specimen of the Recent Stereocidaris leucacantha A. Agassiz and 

 H. L. Clark. 



The peristome is situated centrally in a slight concavity of the 

 base, is large, and includes five prominent oral lobes whose tips- 

 closely approach each other and are separated by deep, narrow 

 ambulacral furrows. The outer surface of each oral lobe is covered 

 with tubercles and is bordered by a slightly raised rim; the walls 

 of the ambulacral furrows are densely packed with very small 

 tubercles of regular size, arranged in rows parallel to the sloping 

 outer surface of the lobe. These features are beautifully preserved 

 on the type, the peristome of which is nearly perfect in all its 

 details. 



The periproct is high on the test, is small, and is situated in a 

 deep, narrow sulcus which flares out and becomes shallow toward the 

 ambitus. 



ReTiiarks. — Perhaps the most closely related American species is 

 Oassidulus porrecttos Clark,^ from the Eipley formation, Exogyra 

 costata zone, in the vicinity of Eufaula, Ala. In form, and in the 



^ Clark, William Bullock, The Mesozoic Echinodermata [of the United States] : U. S. 

 Geol. Survey Mon. 54, p. 76, pi. 31, figs, la-i, 1915. 



