318 THE PALEONTOLOGY OF MINNESOTA. 



[Leptotrypa acervulosa. 



In many respects like L. semipilaris Ulrich, of the Cincinnati rocks, the most 

 striking difference appearing in the number of the diaphragms, these being almost 

 totally absent in that species. An undescribed species, differing chiefly in having 

 much smaller and fewer acanthopores, occurs in the Galena shales. 



Formation and locality. In the lower and perhaps also in the middle third of the Trenton shales 

 at Minneapolis and St. Paul. 



Mus. Reg. No. 6024. 



LEP^OTRYPA ACEKVULOSA, n. sp. 



PLATE XXVII, FIGS. 24 and 25. 



Zoarium occurring as small, irregular or subglobular masses, generally between 

 15 and 20 mm. in diameter and somewhat less in hight. Surface approximately 

 even, but clusters of cells are conspicuously larger than the average, and in one 

 case these are elevated into low monticlues. Zooscia angular, thin-walled, thirteen 

 to fifteen, commonly fourteen of the usual size in 3 mm.; average diameter of aper- 

 tures in the spaces between the clusters about 0.21 mm., of the largest in the 

 clusters 0.35 to 0.4 mm. New tubes are interpolated in a great measure at cor- 

 responding levels through the zoarium, so that immediately above and beneath such 

 a level there may be considerable difference in the average size of the tubes. Dia- 

 phragms from one to one and a half times their length apart except in the mature 

 regions where they are separated by intervals about half as long. Acanthopores 

 very small, in the angles, developed at intervals only, no trace of them being visible 

 in some of the transverse sections. At the surface they are but rarely to be distin- 

 guished. In a single example, however, many of the angles of junction are prom- 

 inent and the walls between them crowned with a closely arranged row of minute 

 papillae. 



L. acervulosa agrees in most respects very closely with an undescribed species 

 occurring at Clarksville, Ohio, in the upper beds of the Hudson river group. Smooth 

 examples of L. (Monotrypa) irregularis Ulrich, also from Ohio, are likewise simulated, 

 but that species is distinguished by having tubes practically without diaphragms. 

 Two other species from the Cincinnati exposures, L. filiosa d'Orb., sp. and L. petasi- 

 formis Nich., sp., are probably the nearest among described species. The first grows 

 in large masses and has well developed monticules, while the second forms hat- 

 shaped or hemispheric zoaria like Prasopora simulatrix. 



Formation and locality. Not uncommon in the Galena shales at Decorah, Iowa. A single speci- 

 men from the same horizon in Goodhue county, Minnesota. Also in the shaly part of the Trenton at 

 Burgin and Frankfort, Kentucky. 



Mus. Reg. No. 8060. 



