Dictyospongidj:. 



387 



horizontal and vertical spicules, as in P. Dawsoni, but no satisfactory 

 evidence of them has been observed. 



Dimensions. A specimen which preserves the upper portion of the cup 

 for a length of 82 mm. has an apertural width of 150 mm. and a diameter at 

 the lower end of 80 mm. Another example which represents the basal and 

 median parts of the sponge, is 90 mm. long, 105 mm. wide at the top, and 

 55 mm. wide at the base. Both of these specimens have been laterally 

 compressed. 



Locality. In the calcareous shales at Crawfordsville, Indiana. 



PlIYSOSPOXGIA. ALTEKNATA, Hall. 

 Plate lxii, Fig. 11. 



1882. Physospoiig ia alternata, Hall. Xotes on the Family Dictyospongida?. 

 Expl. pi. 19, fig. 9. 



1884. Physospongia alternata, Hall. Thirty-fifth Ann. Rept. X. Y. State 

 Musi Nat. Hist., p. 481, pi. xx, fig. 9\ 



The few* specimens of this species which have been observed show a 

 narrow subcylindrical tube with a length of about 40 mm. and a width of 

 25 mm. That these undoubtedly represent a specific form distinct from the 

 others here described is shown, first, in the subequal width of the vertical 

 lateralia, and second, in the comparatively slight development of the alternat- 

 ing elevated and depressed quadrules. 



The vertical and horizontal spicular bands are narrow, subequal in width, 

 about equally distant from one another and hence the quadrules formed by 

 their intersection are nearly square. The number of double rows of squares is 

 but six at the lower part of the specimen, but tow ards its upper part there is 

 a duplication of one of the row~s by the development of a new vertical spicular 

 bundle, such as frequently appear in P. Colletti. It has not been possible to 

 fully investigate the spicular skeleton of this sponge. Some of the vertical 

 lateralia bear clemes similar to those of the other species of Physospoxgia, but 

 no auchorate rods have been observed. Large pentacts lie at the angles of 

 the meshes and small pentacts and smooth-rayed hexacts are found over the 

 quadrules. 



Local if;/. Keokuk group, Crawfordsville, Indiana. 



