270 PALEONTOLOGY OF ILLINOIS. 



This species and varieties is, perhaps, more closely related to 

 Z. trentonensis Worthen sp.*, than to any other of the species 

 found at Dixon, 111. They are easily distinguished by the de- 

 pressed obconical form of that species, and the very short or 

 rudimentary stem. The channels are also separated by wider 

 interspaces than in the present species. 



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

 Trenton limestone, near Dixon, 111. 



ZlTTELELLA LOBATA U. & E. 



PL IV. Figs. 3, 3a, 3b, 3e. 



Sponge of an irregular obconical form, with the upper surface 

 flattened, the sides or lower surface deeply sulcate or irregularly 

 lobate, and abruptly expanded above the stem. The radiating 

 channels of the upper surface are moderately regular, with an 

 average of seven in 10 mm. The cloacal tubes are 1 mm. in 

 diameter, and ten or more in number. The outer portion of 

 the upper surface also exhibits a number of shallow impressions, 

 arranged in an irregularly radiate manner around the centre. 

 On account of the irregular lobate character of the under sur- 

 face the channels here are also irregular. In the perfect state 

 they are covered by a dermal layer, the characters of which have 

 not been ascertained. 



A large specimen has a height above the stem of 30 mm.; the 

 greatest diameter of the upper surface is 90 mm. The stem is 

 compressed and of unknown length. The longest and shortest 

 diameters are, respectively, 22 mm., and 13 mm. 



This well marked species is readily distinguished from all 

 associated forms by the irregularly lobate character of the under 

 surface. 



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

 Trenton limestone near Dixon, 111. 



* Cnemidium? trentonensis, Worthen, 111. Geol. Sur, Bep'ts, Vol. VI. p. 491. 1875. 



