316 THE PALEONTOLOGY OF MINNESOTA. 



INIcbolsouella ponderosaV 



NlCHOLSONELLA PONDEEOSA ? Ulrich. 

 PLATE XXI, FIGS. 13, 14, 20 and 22. 



tNicholsonella ponderosa ULEICH, 1890. Geol. Sur. 111., vol. viii, p. 422, pi. XXXIV, flgs. 5-5d. 



Two specimens only of this form were found by the author at Minneapolis in the 

 lower third or " Stictoporella beds " of the Trenton shales. One is an irregular mass, 

 65 mm. long by 30 to 40 mm. in thickness, presenting the bases of several large 

 branches. The surface is not well preserved, but seems to have been considerably 

 like that of N. laminata. The interior likewise is but illy preserved, and the illustra- 

 tions (figs. 13 and 20) may be objected to on the ground that they are much more 

 distinct than the sections. The "dots" in the interspaces have most probably 

 been drawn too small and too numerous. It seems that two or three should have 

 been united into one, giving an appearance more like fig. 10 of the same plate. 

 Still, enough of the internal characters are to be made out to render the generic 

 reference almost beyond dispute. On protected spots the surface is decidedly spinu- 

 lose. Here about nine zooecial apertures occur in 3 mm. 



The other specimen is a fragment of a branch, about 11 mm. thick and 14 

 to 19 mm. wide. In the shape of the zooecia, their number in a given space, and in 

 the charcter of the interspaces and interior, this specimen is apparently precisely 

 like the first. 



There is nothing decidedly opposing the placing of these specimens with N. pon- 

 derosa, the types of which are from the sponge-layer of the '' Lower Blue" limestone 

 at Dixon, Illinois. Still, better preserved material is desirable before much confi- 

 dence is to be placed in the identification. 



Family AMPLEXOPORID^, Ulrich. 

 Genus LEPTOTRYPA, Ulrich. 



Zoaria varying from thin incrustations to free forms of cliscoidal, spiral, or 

 elongate conical shape; subglobose and irregularly massive species occur also. 

 Zocecial tubes polygonal, with thin walls just appreciably thickened in the mature 

 regions, and a variable number of diaphragms. Acanthopores small, more or less 

 numerous, but almost invariably restricted to the angles of junction between the 

 zooecial tubes. Mesopores wanting. 



Type : L. minima Ulrich, of the Cincinnati group. 



This genus includes forms essentially like those of Amplexopora, Ulrich, only 

 they arise into erect branching zoaria while the species of Leptotrypa never depart 



