248 



THE PALEONTOLOGY OF MINNESOTA. 



[Pfasopora. 



Fig. 15. a and b. vertical and transverse septions of Prasopora selwyni Nicholson, Trenton limestone, 

 Ottawa, Canada; c and d, similar sections of Prasopora oeulata Foord, Galena shales, near Cannon Falls, 

 Minnesota; e and f similar sectioris ot Mesotrypa quebecensis Ami, sp., Trenton limestone. Little Falls, 

 N. Y.; g and h, similar sections of Mesotrypa whiteavesi Nicholson, sp., Trenton limestone, Ottawa, Can. 

 All the figures are xl8. 



Indeed, there are at least ten hemisplieric species, to any one of which the orig- 

 nal of Vanuxem's figure might have belonged. Most of these are species of Prasopora 

 and Mesotrypa, but 1 do not in- the least doubt that Vanuxem, as well as all the other 

 early workers in geology, would have included under one specific name, and perhaps 

 did, also species of Leptotrypa, Monotrypa, and even Crepipora, having a similar mode 

 of growth. In the absence of his illustrated specimen, and the utter impossibility of 

 deciding permanently to which of these various forms it belonged, it seems to me 

 not only desirable but necessary to drop the names lycopodites and lycoperdon, so far 

 as their application to fossils of the types in question is concerned. 



Formation and locality.— The typical form of the species Is one of the most abundant and character-: 

 istic fossils of the shaly part of the Trenton group of central Kentucky. It occurs also at Nashville, 

 Tennessee, and in the Galena limestone at Neenah and Oshkosh, Wisconsin, and Decorah, Iowa. In 

 Minnesota it is abundant in the upper third of the Trenton shales at St. Paul, anti rather rarely at other 

 localities in the state. Also in the upper part of the Galena shales at Kenyon and other points in 

 Goodhue county. The exact horizon of certain specimens in the state collection labeled Minneapolis, 

 Lanesboro and Mantorville, is somewhat doubtful. The variety orientalis is common in the Trenton lime- 

 stone at Ottawa, Peterboro, and other localities in Canada, and at Trenton Falls, New York. 



Mus Beg. Nos. 4041, 5124, 5532, 5986-5988, 6786, 7570, 7571. 



