FROM THE CARBONIFEROUS LIMESTONE OF IOWA. 



501 



GENUS CYATHOCRINUS. Miller. 



CYATHOCRINUS IOWENSIS. (N. S.) 

 (Tab. V. a, fig. 11, a, b, c.) 



Body globose. Basal plate rather small, pentagonal, composed of five plates, closely adhering among 

 themselves, flattened, with a small hemispherical cavity for the insertion of the column, having a small 

 round perforation in the centre ; superior angles bent slightly upwards. First scries of perisomic plates 

 five, of which four are pentagonal, inclining, however, to a subhexagonal form ; and one hexagonal. These 

 plates are somewhat massive and tumid in their centres. The second scries is composed of six plates, five 

 are pentagonal, support the arms and rest on the oblique upper edges of the first series ; the sixth, which 

 is hexagonal, is placed on the superior truncated edge of the hexagonal plate of the first series, and sup- 

 ports on its upper edges three small irregular plates. The articular facets for the attachment of the arms 

 are horseshoe-shaped, moderately largo, concave, and have a deep angular notch superiorly. The external 

 surface of all the plates which compose the body are finely corrugated, giving to the species a very neat 

 appearance. 



Column, arms, and abdominal plates unknown. 



Formation and localities. — It occurs at Burlington, Iowa, in the carboniferous limestone, whence we 

 have been so fortunate as to obtain several specimens. We arc not aware of its having been found else- 

 where. 



CYATHOCRINUS CORNUTUS. (N. 8.) 

 (Tab. V. a, fig. 8, a, b.) 



Basal plate small, pentagonal, composed of five subrhomboidal plates, firmly adhering among them- 

 selves; flattened or slightly concave, with a small pentapetalous central perforation. First series of 

 perisomic plates five, four of which are pentagonal and one hexagonal. Each plate is lengthened into a 

 process approaching to a conical form, which projects downwards and outwards for some distance below 

 the plane of the basal plate, so that when a side view of the visceral cup is taken, this plate is not visible. 

 The second series consists of six massive plates, of which five support the arms, and rest by their lower 

 salient angles in the re-entering angles formed by the union of the first series. The arm-bearing plates 

 are conical in their centres, and present, at their superior edges, a large bevelled surface, which is some- 

 what of a semilunar shape, and slightly concave for the insertion of the arms. 



Column, arms, and abdominal jflates undiscovered. It is associated with the preceding species at 

 Burlington, where it is exceedingly rare ; only a single specimen having rewarded our search. 



GENUS PENTREMITES. Say. 



PENTREMITES* NORWOODII. (N. S.) 

 (Tab. V. a, fig. 13, b, c.) 



The general form of this species is globose, and the whole surface between the so-called ambulacral 

 spaces is thickly studded with small granulas, very regularly arranged in longitudinal rows. At the base 

 a profound funnel-shaped cavity is observable. 



The basal plate (pelvis) is small and lines about one-half of this funnel-shaped cavity, at the apex of 

 which is a small circular impression for the insertion of a column. This pelvis is composed of three 

 pieces, two pentagonal and one trapezoidal. 



Costcds five ; elongated, equal, extending along the whole height of the body, bent upwards inferiorly 

 to articulate with the pelvic plates in the fannel-shaped cavity. The summit of each plate is obliquely 

 truncated on both sides of the ambulacra, so that when these plates are united together, five re-entering 

 angles are formed, in which rest the inferior salient angles of the superior plates. A longitudinal medial 



* It is probable that this and the following species will constitute a new genus. 



