DESCRIPTIONS OP Tin: SPECIES. 165 



of the radial plates. The consequence of this is that the bydrospire-folds appeal 

 much shorter on the inside of the plate than the ambulacrum dues on the outside 

 (PI. III. figs. 5-9); and the markings representing the ambulacra on the internal 

 casts do not reach much below the equator, although the external ambulacra are ;i- 

 long as the calyx (PI. III. rig. 4). The way in which this is caused by an ingrowth 

 of the sides of the radial sinus is well shown in PI. XVIII. rigs. 7, 8. 



Locality and Horizon. Spergen Hill, Indiana: Warsaw Limestone, St. Louis Group, 

 Subcarboniferous. 



Pentremites sulcatus, Roemer, sp. 

 (PI. I. figs. 8-10; PI. II. fig. 31; PI. XVI. fig. 20; PI. XVIII. fig. 5.) 



Pentatrematitcs sulcatus, Roemer, Archiv f. Naturgescb. 1851, Jahrg. xvii. Bd. i. p. 354, 



t. 6. f. 10 a-c. 

 Pentatrematites sulcatus, Roemer in Bronn's Lctluca Gcogn. Dritte Aufl. 1832-51, Tbeil ii. 



p. 282, t. V. f. 9, a $ b. 

 Pentremites sulcatus, Sbumard, Trans. St. Louis Acad. Sci. 1858, vol. i. no. 2, pp. 2 13 and 



216; ibid. 1865, vol. ii. no. 2, p. 385. 

 Pentremites sulcatus, Lyon and Casseday, Proc. American Acad. 18G0, vol. iv. p. 298. 

 Pentatremitcs sulcatus, Bronn, Klassen und Ordn. Tbier-Reichs, 1860, Bd. ii. t. 23. f. 1 P-J. 

 Pentremites sulcatus, Dujardin & Ilupe, Hist. Nat. Zoopb. Eebinod. 1862, p. 91. 



Sp. Char. Calyx large, subglobose ; summit truncate ; peristome concave ; base 

 short and obtusely pointed ; section strongly pentagonal, the very concave am- 

 bulacra with the concave interradial areas giving rise to ten re-entering angles ; 

 periphery almost equatorial. Basal plates large, forming a shallow expanded cup ; 

 interbasal sutures in slight concavities. Radial plates large, oblong, and very pro- 

 minent, much arched ; bodies less than a third the length of the limbs, subcarinate 

 in the middle line ; limbs moderately long, with high, sloping, and more or less con- 

 cave sides, obliquely truncated above ; interradial sutures in deep concavities; sinuses 

 deep, subpetaloid, with very sbarp erect margins ; lips simple. Deltoid plates elon- 

 gately rhombic, with sharp margins and a concave surface, and placed on a level with 

 the summit ; radio-deltoid sutures straight or slightly sigmoidal. Ambulacra deeply 

 inserted in the sinuses, much curved longitudinally, surface concave, the sides right 

 and left of the ambulacral groove sloping inwards towards the latter, except for a 

 very narrow margin immediately below the edge of the sinus, which is nearly hori- 

 zontal ; lancet-plate equal in width to the two rows of the side plates ; ambulacral 

 groove wide and shallow, and the lateral grooves almost horizontal ; side plates about 

 sixty-five, large and oblong. Four or five hydrospire-folds on each side. Spiracles 

 large, rhombic-pyriform ; septa incomplete, their central ends being represented by 

 rounded tubercles. Mouth small. Ornament of the usual character. 



Remarks. P. sulcatus belongs to a well-deriued section of the genus which contains 



