Spkcijb ok the Kkokuk Group. 198 



ghrioHd, and other species, we have to conclude that it belongs to a large 

 hexact or pentact whose precise position in the skelet<)n still remains in douht 



Smooth, elongate 8ili<piate diacts (figure -41) of small size are occasionally 

 f(nmd among the parenchymalia. 



After careful search tliis species has afforded no evidence of tirahels such 

 as occur in J*. Colletti and Clewllctija (jloriuna. Nevertheless it seems prol>- 

 able that they exist, though they may be of great raiity. 



Dimensions. The size of this species, in ctunparison with its closest ally, 

 P. Colletti, is always small. An individual of rather large dimensions has a 

 length of 70 mm., an apertural diameter of 80 mm., and a basal diameter (»f 

 30 ram. Fragments of somewhat larger examples have been observed. An 

 average specimen which seems to be complete, is 45 mm. in length, has a bjisal 

 width of 50 mm., contracting above this to a width of 44 ram. and expanding 

 again to an apertural diameter of 00 ram. 



Localitij. Physosjnnigia Dawsoni is known only from the calcareous shales 

 of the Keokuk group at Crawfordsville and Indian Creek, Indiana. 



PiiYsospowGiA Colletti, Hall. 



Plate i-xiii, Flos. 1-7. 



1884. Physosponijia Colletti, Hall. Thirty-fifth Ann. Rept. N. Y. State 

 Mus. Nat. Hist, p. 480, pi. xx, fig. 7. 



Sponge large, rapidly, and sometimes unsymmetrically e.vpanding from a 

 broad base to a wide aperture. 



Surface highly nodose, similar in structure and aspect to that of P. 

 Dawsoni, but with nodes of much greater size, and with more frequent irreg- 

 ularities in their ari\angement. 



Peticuliim. The 2)riraary and secondary vertical bundles are of very 

 unequal size. The former are broad and ct)mpact over the lower portion of 

 the sponge but become diffuse above, spreading into a fan-like brush near the 

 aperture and obscuring thereby some of the main quadrules. Over the median 

 and lower portion of the cup the quadrules are nearly square but toward the 

 aperture both nodes and concavities become transverse, the horizontal diame- 

 ter increasing and the vertical diameter lessening, until each division becomes 

 very narrow. Thereupon ensues a multiplication in the number of vertical 

 rows of nodes and depressions, the two rows of any one of the main vertical 

 divisions of the surface increasing to four, and the area occupied by each large 

 node or depression over the body of the cup bears two small nodes and cor- 

 responding depressions. This duplication of the vertical rows of quadrules is 



