116 THE PALEONTOLOGY OF MINNESOTA. 



[Stomatopora. 



matter, the former in their mature or ultimate development, are much nearer Berenicea 

 (Lamouroux, Haime, Zittel and others ; Diastopora of Busk and other British authors). 

 Sharply defined genera are an impossibility in nature. She follows paths altogether 

 too intricate to be expressed in a system of classification. The best result that we 

 can obtain must be a happy medium between convenience and natural affinity. Con- 

 venience, and stability as well, are surely sacrificed when we throw together a number 

 of genera and then divide the composite genus, that has now been made to assume 

 the rank of very nearly a family, into sections of questionable utility that no one is 

 obliged to recognize, because they have no established 'validity in any system of 

 classification. Is it not better, because it is convenient and saves time, to have it 

 understood at once that when one says Stomatopora, he refers to uniserial forms; 

 Prohoscina, to forms with similar zooecia but partly immersed and in two or more 

 series, and Berenicea, to such as have them forming entire, flabellate, circular or 

 irregular crusts ? 



The only change from the arrangement here retained that I am willing to enter 

 into, and for which good and probably sufficient reasons can be advanced, is one 

 that would drop Prohoscina, leaving Stomatopora to stand as at present for the 

 uniserial species, and extend Berenicea so as to include the ground now occupied 

 by Prohoscina. 



Stomatopora tenuissima Ulrich. 



PLATE I, FIGS. 6 and 7. 



Stomatopora tenuissima Uleich, 1890. Jour. Gin. Soc. Nat. Hist., vol. xii, p. 175. 



Original description.-^" Zo'drixum. adnate, consisting of frequently branching 

 uniserially arranged zooecia. Zooecia exceedingly slender, about seven in 8 mm. 

 each from 1.0 to 1.5 mm. long, usually increasing very gradually from the proximal 

 end, where the diameter is about 0.04 mm., to near the slightly bulbous anterior or 

 upper end, which varies from 0.11 to 0.18 mm. in diameter. Aperture circular, small 

 about 0.05 mm. in diameter, situated very near the anterior end of the zooecium. 



" This and S. turgida illustrate the extremes of difference in shape and size of 

 the zocoeia of Stomatopora. so far noticed. S. tenuissima is closely related to S. prout- 

 ana Miller, but its zooecia are much longer. Miller's species, with scarcely any 

 modification, ranges from low in the Trenton (Birdseye limestone) to the top of the 

 Hudson River group. 



Formation nad locality.— TowzxA the top" of the Utica horizon of the Hudson River group at Cincin- 

 nati, Ohio, 150 to 175 feet above low water mark in the Ohio river. 



