PALEONTOLOGY OF IOWA. 693 



from forty to fifty on each side, nearly rectangular to the 

 area, and slightly curving upwards on the median line. Mouth 

 pentangular : ovarian apertures broad oval ; summit convex. 



This species resembles in many respects the P. pyriformis ; but is more truncate 

 at the base, and the initial joint of the column is spreading above, and forms a more 

 conspicuous feature. The specimens before me do not offer gradations from one species 

 to the other, as suggested by Dr. RCEMER. 



Fig. 13 a. Lateral view of a specimen. Fig. 13 b. Basal view of the same. 



Geological formation and localities. In the Kaskaskia limestone : Chester, 

 Illinois ; Huntsville, Alabama, etc. 



Pentremites pyriformis. 



PLATE XXV. FIG. 16. 

 Pentremites pyriformis : SAY, 1822, Jour. Acad. Sci. Philadelphia, Vol. iv, p. 294. 



TKOOST, Trans. Geol. Soc. Pennsylvania, Vol. i, pa. 228, pi. 10. 

 SOWERBY, Zoological Journal, Vol. ii, p. 315. 



RCEMER, Monog. Blastoidese, pa. 354, pi. 5, f. 9 a, 6, c. 



BODY pyriform, the greatest diameter in the middle, and 

 tapering to both extremities; the summit more obtuse and 

 rounded, obtusely pentangular below the pseudambulacral 

 areas, with the sides flat : base narrow, with the upper joint 

 of the column usually remaining attached. Basal plates 

 forming a pentagonal shallow vase. Radial plates spreading 

 and ascending, angular along the middle at the base, deeply 

 furcate, slightly concave along the lateral sutures. Interradial 

 plates narrow lanceolate, reaching nearly to the summit. 

 Pseudambulacral areas lanceolate, gradually enlarging from 

 the base, concave towards the median line, or sometimes flat : 

 the number of pore-pieces varies from thirty to fifty on each 

 side of the median line. Mouth pentagonal : ovarian aper- 

 tures closely arranged, often somewhat transversely oval. 



This species has been so fully described, that it is unnecessary to enter into detail 

 in this place. The specimens before me seem clearly distinct from P.florealis, while 

 there is much difficulty in separating them from P. tennesseeee of TROOST, which 

 latter is perhaps identical with P. koninckana of HALL. Should this suggestion be 

 verified, the latter name will give place to that of Dr. TROOST. 



Fig. 16. A specimen of small or medium size, with a portion of the column attached. 

 Geological formation and localities. In the Kaskaskia limestone : Chester, 

 Illinois ; near Huntsville, Alabama, etc. 



