208 MESOZOIC AND CENOZOIC ECHINODEKMATA OF THE UNITED STATES. 



The interambulacral areas, except the posterior area, are narrow in the petaloid region, 

 wider in the marginal region; the posterior interambulacral area is wider and its plates differ 

 considerably in form from those of the other areas, because of the presence of the lunule. The 

 whole surface of the test is covered with small uniform tubercles which are larger on the under- 

 surface and inside the lunule. 



The apical system is excentric anteriorly, in front of and below the apex on the more or less 

 steeply sloping anterior side of the central mound. The madreporite is large, stellate or sub- 

 pentagonal, nearly flush with the surface. There are five genital pores a short distance away 

 from the points of the madreporic star, their relative positions varying somewhat, and five 

 small radial plates each perforated by a small pore, on the proximal side of which there is a very 

 small swelling. The posterior genital pore is sometimes somewhat displaced from the median 

 line. 



The peristome is small, subcircular to subpentagonal, excentric anteriorly; the ambulacral 

 furrows rather deep, simple and straight for a short distance from the peristome, then forking, 

 each pair of branches diverging somewhat, the three anterior pairs more so than the posterior 

 two, extending to the margin and ending close alongside of the marginal notches. Each branch 

 gives off one side branch on the outside at nearly right angles about halfway from the peristome 

 to the margin, which soon bend and proceed to the margin. A very thin ridge extends out from 

 the peristome along the middle of the short unbranched portion of each ambulacral furrow. 



The periproct is very small, much smaller than the peristome, usually elliptical or sub- 

 elliptical, sometimes subcircular or subpyrif orm, situated usually on the sloping edge of the lunule 

 nearest the peristome, sometimes on the inner wall of the lunule, but near the under surface of 

 the test. 



This species presents variable features which illustrate in an interesting way changes due to 

 the development of the individual. As the forms increase in size and age the lunule enlarges and 

 becomes more elongate and irregular, the posterior marginal notches become less flaring and tend 

 to close, the posterior edge changes from a truncated one to one more and more convexly rounded, 

 the posterior end becomes at first relatively broader then relatively narrower than the anterior 

 end, the height of the central mound and thickness of the margin increase, the corrugations on 

 the upper surface become more accentuated, and irregularities appear in the poriferous zones. 

 Lack of space forbids a more complete discussion of these features here; but a comparison of the 

 figures given will bring them out in a stronger light. Specimen A, for instance, presents geruntic 

 features, the effect of the elongation of the lunule in pushmg out and rounding the. posterior 

 border, nearly closing the posterior notches and so changing the marginal outline as to make the 

 form seem at least varietal in value if not a different species. 



Related forms . — The only American fossil echinoid resembling this species is E. tenuis Kew, 2 

 from the upper Miocene or lower Pliocene of the Pacific coast. E. macrophora is easily separated 

 by its larger lunule, shallower anterior notches, posterior petals curving around the lunule, and 

 having the periproct at the edge of the lunule. The recent species Encope grandis L. Agassiz, 

 reported by A. Agassiz 1 from the Gulf of California, is the most closely related to the present 

 form, the very features which A. Agassiz notes as remarkable in E. grandis being those most 

 characteristic of E. macrophora. E. grandis differs, however, in having all five marginal notches, 

 and especially the three anterior ones, larger and more deeply incised, in having wider interpo- 

 riferous areas, and the posterior margin concave. Encope emarginata Agassiz, a recent species 

 from the coast of Brazil and the West Indies, is similar in general outline to E. macrophora, the 

 young forms of the two species being quite similar, although the lunule of the young E. macro- 

 phora is usually more circular than that of the young E. emarginata. The older forms of E. 

 emarginata also differ hi that the marginal notches become lunules, a change which appears 

 never to take place in E. macrophora. Possibly the present fossil form may be ancestral to E. 

 emarginata. Encope cise De Cartazar, from the upper Miocene of Cuba, presents some points 

 of similarity to the present species, but its lunule is smaller and more rectangular in form, its 



i Revision of the Echini, p. 545 and PI. XIII, fig. d. 



2 The description of E. tenuis Kew appeared while the present work was in press. See California Univ. Dept. Geology Bull., vol. 8, No. 5, 

 pp. 47-48, PI. I, fig. 1, and PI. II, fig. 1, 1914. 



