SPONGES. 275 



ate<] sponges, it was deemed advisable to name and illustrate 

 them. The form is obliquely conical, about a.s wide as high; 

 the cup very deep, with the margins rounded. Sides of cup pre- 

 senting the apertures of large radiating canals, arranged seri- 

 ally in the bottom of vertical channels, four or five in 10 mm. 

 The outer surface of the sponge wall is much weathered, but 

 preserves enough to show that though the radiating canals 

 pass through the wall they are less regularly arranged here 

 than on the inner surface. The spaces between the canals are 

 poriferous, but the form of the spicules could not be determined, 

 with certainty. A transparent section seems to show, however, 

 that they are not unlike those of the ANTHASPIDELLID.E. Sponge 

 wall gradually increasing in thickness from below up\vards. 

 The greatest thickness, 10 mm., is in the upper one-third of the 

 height. 



This sponge is placed provisionally in the genus Calathium of 

 Billings, because it is most probably congeneric with his C. 

 ruiicidense, from the Chazy. Question signs are added because 

 we believe C. formosuw, the type of the genus, is generically 

 distinct from these forms, but till the spicular structure of the 

 various species has been determined, it will be impracticable to 

 separate the groups. Perhaps the genus Zittelella should be 

 extended so that it would include species of this type. 



Position and locality: Twenty-five feet above the base of the 

 Trenton limestone, near Dixon, Illinois. 



HINDI A IX.EQVALIS F. .V: E. 



PI. H. fig. 4. 4a, 4b. 



Sponge free, of spherical form, with the surface evenly rounded. 

 The diameter of the largest specimen is 13 mm. Other examples 

 apparently belonging to the same species, vary from 7 to 10 

 mm. 



The centre of the sponge is occupied by loose tissue, from 

 which extend small straight canals to all parts of the surface. 

 The radiate canals increase in number, and very slightly in size, 

 a.s the sponge grows larger, are sub-circular in section, and vary 



