594 



NEW SPECIES OF CRINOIDEA, 



angles are inserted in the retreating angles formed by the union of the hexagonal plates of the first series ; 

 two are irregularly heptagonal, and one hexagonal : these repose on the upper edges of the heptagonal 

 plate of the first series. Each of the above-mentioned quadrangular plates is surmounted by a widened 

 pentagonal plate, which again supports on its oblique upper edges two short irregular pieces, sub-hexagonal 

 or pentagonal, with their superior margins slightly concave to accommodate the arm-bearing plates, which 

 are small and somewhat horseshoe-shaped. All the pieces which we have mentioned above the basal 

 plate are elevated in their centres, which gives to the surface of the visceral cup an uneven appearance. 



The coronal integument is made up of numerous polygonal plates. The central one is a little larger 

 than the rest, and is garnished with a spinous process, which is often produced to half an inch in length ; 

 the others are usually tumid in their centres and wrinkled ; in some specimens, however, they are furnished 

 with projecting tubercles, some of which are flattened and divided into two or more points. 



Mouth sub-central, protrusive but not proboscidiform. It is situated near the inner extremity of a 

 prominent ridge composed of small, irregularly-shaped plates. This ridge commences at the central spinous 

 plate, and terminates at the outer border of the cup between two of the arms. 



Arms twelve, bifurcations unknown. Column undiscovered. 



It occurs rather abundantly in the subcarboniferous limestone at Burlington and Augusta, Iowa. 



MEGISTOCRINUS. (N. G.) 



Generic character. — Basal plate tripartite, hexagonal, divisions equal. First series of plates six, five 

 hexagonal, and one pentagonal ; second series thirteen, hexagonal ; third series nineteen, five pentagonal, 

 eight hexagonal, six heptagonal. These are surmounted by six ranges of polygonal plates, each range 

 becoming successively smaller, and the plates more numerous in the ascending order. Coronal integu- 

 ment composed of numerous polygonal plates. Proboscis a little below the superior rim, short and 

 slender. 



MEGISTOCRINUS EVANSII. (N. S.) 

 (Tab. V. a, fig. 3, a, b.) 

 Synonym. — Actinocrinus Evansii, vol. ii., part i., p. 68, Jour. Acad. Nat. Sci. 



Specific character. — The body of this fine species has the form of an inverted truncated cone, with a 

 moderately rounded base. Basal plate large, somewhat massive, flattened, slightly concave near the 

 margin, moderately convex towards the centre. Impression for the attachment of the column large, 

 occupying nearly one-half the diameter of the plate, slightly excavated and striated on the margin, per- 

 foration largo, obscurely pentagonal. First series of plates large, moderately convex, bent inwards and 

 slightly upwards near their inferior margins, projecting below the plane of the basal plate, and not 

 visible on the side view of the fossil. All the plates forming the sides of the cup are smooth, and 

 slightly convex on the surface. Coronal slightly elevated, pieces of various dimensions, the larger ones 

 mammillated in the centre. 



Proboscis short and slender ; column and arms unknown. 



Dimensions. — Height, twenty-five lines ; width at summit, thirty-two lines ; width at base, thirteen 

 lines ; diameter of basal plate, seven lines. 



Formation and locedity. — It occurs with the preceding species in the lower series of carboniferous 

 limestone at Burlington, Iowa. For the magnificent specimen figured we are indebted to John Evans of 

 the United States Geological Corps, and to him we have dedicated it. 



PLATYCRINUS. Miller. 



PLATYCRINUS AMERICANUS. (N. S.) 

 (Tab. V. b, fig. 1, a, b.) 



Calyx. — Subglobose, surface ornamented with numerous prominent granulse. Based plate pentagonal, 

 flattened; surface for the attachment of the column small, round, finely striated in radii, with a minute 

 central perforation. From the edge of this surface five principal rows of granulas radiate to each angle 

 of the plate, the intervening spaces being likewise granulated. Superior plates five, rather broad, in- 

 creasing slightly in width from below upwards ; articular facet for the arms small and shallow. The 

 granulse are usually disposed over the surface of these plates, as follows : a row commences at each of 



