NATURAL SCIENCES OF PHILADELPHIA. 33 



terradials more than twice as long as wide, the widest part being below, while 

 the central region is much contracted, and the upper part, like that of the 

 anal piece, somewhat dart-shaped, and a little concave, with a smaller tuber- 

 cle occupying the middle of the little concavity. 



So-called pseudo-ambulacral fields rather narrow, somewhat convex, with 

 mesial or ambulacral furrows rather wide and deep, particularly above the 

 middle; pore or arm-pieces, about twenty-two on each side of each area ; lan- 

 cet pieces very narrow, but thick, and rather deeply furrowed along the mid- 

 dle above, where they form the bottom of the ambulacral furrows; farther 

 down, the pore pieces close in so as nearly or quite to cover th lancet pieces 

 at the lower end. Elongated slits corresponding to the openings usually 

 called ovarian apertures in Pentremitcs, widest at the upper end, and extending 

 down apparently three-fourths of the length of the pseudo-ambulacral areas, 

 so very close to the margins of the latter as scarcely to leave more than a 

 thin intervening space above, and apparently none below. Central hiatus 

 very small, and doubtless covered by minute plates in perfect specimens. 



Surface distinctly ornamented with very regular, well-defined stria 1 , run- 

 ning parallel to the upper margins of the basal pieces, and to the inferior and 

 lateral margins of the radials. Along the margins of the pseudo-ambulacral 

 areas, narrow flattened, or very slightly concave spaces are seen extending 

 along the surface of the radial pieces, and corresponding to the rather broad, 

 deep furrows seen occupying the same position in the typical species, C. 

 stelliformis. (Column and pinnulae unknown.) 



Height, 0-60 inch ; breadth, about 0-50 inch. 



This species, although agreeing with C. stelliformis in the important charac- 

 ters distinguishing this genus from Penlremites and Codaster, differs so materi- 

 ally in form and other specific characters, as to render a comparison unneces- 

 sary. In general form it much more nearly resembles the true Pentremite.t 

 than the typical form of Codonites does. It must be very rare, as we are not 

 aware that more thau the one specimen has ever been found. 



Locality and position. Lower division of the Burlington group of the Lower 

 Carboniferous, at Burlington, Iowa. Mr. Wachsmuth's collection. 



Pentremites Burlingtonensis, M. and W. 



Body attaining a medium size, ovoid, or ovoid-subglobose, depressed and 

 short below, and rounded and more produced above. Supplementary base 

 very small, or only one-fourth as wide as the base, rounded and firmly anchy- 

 losed to the true base ; short, or apparently composed of not more than three 

 anchylosed segments from the upper end of the column. Base of moderate 

 size, much depressed, or having the form of a pentagonal dish. Radial pieces 

 once and a half as long as wide, rather narrow below, and widening upward 

 to near the middle, above which they are very slightly contracted to the top ; 

 each divided three-fourths of its length by its rather wide pseudo-ambulacral 

 sinus. Anal and interradial pieces very small, exposed part presenting an 

 elongate rhombic outline, the upper part being more elongate and acute thau 

 the Tower. So-called pseudo-ambulacral areas* wide, moderately convex, 

 taperino- rather gradually below the middle, and more abruptly above ; so- 

 called nore pieces about 35 on each side of each area, less than half as long, 

 transversely, as the breadth of the exposed part of the lancet pieces at their 

 widest part, nearly transverse above, but becoming somewhat oblique toward the 



lower part of the area ; supplementary pore pieces small. Lancet pieces ex- 

 posing a wide, lanceolate form, being widest above the middle, gradually ta 

 pering below, and contracting abruptly above; each with its mesial or amba 

 lacral furrow rather wide and deep, and minutely crenate within ; tra n a vers 



* Although we use here the u 8 ual term for these parts, we really regard them as recum- 

 bent arms, similar to those seen in some Cystoidea. 



1870.] 3 



rse 



