PLIOCEXE ECHINODEKMATA. 219 



The interambulacral areas are narrow throughout their whole length, though wider between 

 the ends of the petals than elsewhere, much narrower than the ambulacral areas. The whole 

 surface of the test is thickly set with small tubercles which are somewhat larger on the under 

 surface. 



The apical system is central, sloping downward anteriorly from the apex; the madreporite 

 large, pentagonal, slightly depressed. There are five genital pores situated a short distance 

 from the madreporite ; and there are five small radial plates at the edge of the madreporite, per- 

 forated by minute pores. 



The peristome is large, subpentagonal, slightly excentric posteriorly at the deepest point 

 of the deep concavity on the under surface. The ambulacral furrows are simple, straight 

 shallow grooves extending from the peristome almost to the margin, which are deeper midway 

 than toward the peristome. 



The periproct is rather large, circular, inframarginal, almost marginal. 



Related forms. — D. dalli is very closely related to the recent American form generally known 

 as Echinanthus rosaceus (which, if Duncan be followed, should be Diplothecanthus rosaceus), 

 differing from it chiefly in being relatively higher, in having the apex slightly excentric posteriorly 

 and ang'ular, with a straighter slope anteriorly and a steeper slope posteriorly, in having the 

 apical system sloping downward anteriorly, and in having the interporiferous areas more tumid 

 and coalescing around the madreporite. D. dalli rather closely resembles in many features the 

 foreign forms Clypeaster crassicostatus 1 Agassiz, from the Miocene of Austria-Hungary, Italy, 

 and Corsica, but differs from it in being less elongate longitudinally and more elevated, in hav- 

 ing more difference between its anterior and posterior slope, and in having its petals broader, 

 slightly less open and somewhat longer. 



Locality. — Near Fort Thompson, Caloosahatchee River, Fla. 



Geologic A-omoji.^Caloosahatchee marl, Pliocene. 



Collection. — U. S. National Museum (164670). Collected by "W. H. Dall, after whom the 

 species is named. 



Diplothecanthus rosaceus (Lamarck). 



Plate CII, figures la-b; Plate CIII, figures la-b 



Echinus reticulatus Linne, 1758, Systema naturae, p. 3191. 



Clypeaster rosaceus Lamarck, 1840, Animaux sans vertebres, 2d ed., p. 289. 



Echinanthus rosaceus A. Agassiz, 1872, Revision of the Echini, pp. 106, 311, 514. 



Description. — This well-known recent species is so fully described elsewhere it is needless 

 to give a detailed description here. The specimen here figured was reported as found in the 

 Pliocene deposits of Florida. The test is very large; pentagonal in marginal outline, the corners 

 of the pentagon being rounded and the sides and posterior end slightly concave; somewhat 

 longer than broad, pointed anteriorly; margin thick and rounded opposite the petals, less so 

 between them. The upper surface is convex, moderately high, of uniform height at the highest 

 parts of each of the petals. The apex is central, coincident with the apical system, and the 

 upper surface is nearly level for nearly an inch out from the center in rather steep curves along 

 the ambulacral areas and in steep nearly straight lines along the interambulacral areas to the 

 margin. The outline along a longitudinal median section is nearly level for the central third 

 of the length of the test whence it slopes nearly equally to each end. The under surface is 

 nearly flat around the margin and rather strongly concave around the peristome, where it is 

 less than one-half the height of the test. 



The ambulacral areas are very wide, the dorsal portions petaloid. The petals are very 

 large, very broad, moderately tumid, well apart at the ends, subequal in length. The poriferous 

 zones are very wide, the inner row of pores moderately elevated above the outer. 



The interambulacral areas are very narrow, especially at the margin, where they are only 

 about one-third as wide as the ambulacral areas. 



1 See Michelin's Monographic des Clypi?astres, p. 115, PI. XVII, figs. la-f. 



