MIOCENE ECHINODEEMATA. 205 



Description. — This beautiful Mellita, first reported and described by Ravenel in 1841, is 

 probably the oldest representative of the genus, as it undoubtedly existed in America in Mio- 

 cene time. Hitherto the genus has not been positively known to have existed prior to the 

 Pliocene. The species is rather rare, only a few specimens having been reported up to the 

 present time. The test is small to very large in size, ranging from 1 to 6 inches in diameter. 

 In marginal outline it is somewhat variable, being either subcircular, subpentagonal, or broadly 

 subovate. It is usually about as long as broad; broadest between the anterior and posterior 

 pair of petals, usually about the middle, but sometimes back of the middle of the test; rounded 

 or truncated posteriorly. There are six lunules, one opposite each petal and very near the 

 margin and one in the middle of the posterior ambulacrum, distant from the margin. The 

 three anterior lunules are short and either pyriform or narrowly oblong, the posterior pair 

 longer and usually narrowly oblong, and the odd posterior one much longer and frequently 

 wider than all of the others, and either narrowly oblong or elongate subpyriform or elongate 

 subelliptical. In young specimens the odd posterior lunule is much longer and more con- 

 spicuous relatively than in older ones. The whole form is greatly depressed, the upper surface 

 rising gradually from the margin to the very low apex which is either central, slightly excentric 

 anteriorly or excentric posteriorly, and rarely rises to a height of half an inch in even the largest 

 specimens. The margin is thin, sometimes with faint notches opposite the posterior paired 

 petals. The under surface is flat, or nearly so. 



The ambulacral areas are relatively narrow in the petaloid dorsal portions, wide between 

 the ends of the petals and the margin where they are wider than the interambulacral areas, 

 narrowing again at the margin. The petals are large, and somewhat variable, extending half- 

 way cr decidedly more or less than halfway to the margin; subelliptical to subspatulate in form; 

 usually narrower than those of Mellita pentapora; the posterior pair longer than the others, 

 which are subequal in length. The poriferous zones are broad, equal to or broader than the 

 interporiferous areas; pores oval, pairs of pores conjugated by very narrow, flexuous grooves. 



The interambulacral areas are broad, broadest at the margin, where they are wider than 

 the ambulacral areas. The surface of the test is closely set with very small, imperforate 

 tubercles, set in deep scrobicules. The tubercles are larger on the under surface except along 

 and near the ambulacral furrows. 



The apical system is excentric anteriorly, large and stellate; four genital pores at the tips 

 of the points of the star, the two posterior farthest apart; five small pores at the inner ends of 

 the reentrant angles of the star. 



The peristome is small, subcircular, excentric anteriorly; the ambulacral furrows simple 

 and straight near the peristome, then forking, each pair of branches diverging and again con- 

 verging near the margin so as to surround the lunules. 



The periproct is very small, elliptical, between the inner end of the odd posterior lunule 

 and the peristome. 



Related forms. — M. caroliniana is closely related to M. pentapora, which is readily sepa- 

 rated by its having only five lunules, by the greater height and more anterior position of its 

 apex, and by having its lunules subequal in length and farther from the margin. M. caroliniana 

 is still more closely related to the recent species M. sexforis A. Agassiz, which, however, differs 

 in having its five ambulacral lunules all of the same length and its odd posterior lunule a little 

 shorter than the others ; another difference is that the distance between the pairs of food grooves 

 in M. sexforis is greater than it is in M. caroliniana. 



Localities. — Ravenel's type came from The Grove, Cooper River, 17 miles from Charleston, 

 S. C. The large form figured in this paper came from South Carolina; but the exact locality is 

 not known. Other localities are Goose Creek, Cooper River, and Bostick Landing, Great 

 Peedee River, S. C. ; Wilmington, and 3 miles north of Grifton, Pitt County, N. C. ; Yorktown, Va. 



Geologic horizon. — Duplin marl in South Carolina, and Yorktown formation, in North 

 Carolina and Virginia, both upper Miocene. 



Collections. — Academy of Natural Sciences of Philadelphia (1083) ; American Museum of 

 Natural History; U. S. National Museum. 

 39800°— 15 14 



