296 THE PALEONTOLOGY OF MINNESOTA. 



[Hatostoma wlnc-hrlli. 



Internal characters: Being an exceedingly common and superficially variable 

 species, over thirty sets of thin sections were prepared. These prove the species 

 constant in most of the characters shown in vertical sections, and decidedly variable 

 in tangential sections. It should, however, be stated that many of the specimens 

 sectioned exhibited some external peculiarity or deviation from the ordinary types 

 of the species. In the axial region of vertical sections the tubes are thin-walled 



* 



and crossed by diaphragms from one to three times their diameter distant from 

 each other. But in the attenuate proximal ends of the tubes the diaphragms are 

 always closer than after the tubes have attained their full size. In entering the 

 peripheral region, the width of which depends upon age, the tubes bend outward 

 rather abruptly, proceeding thereafter directly to the surface. In the turn the 

 diaphragms become more numerous and, though generally straight and complete, 

 not infrequently exhibit a tendency to coalesce with each other. In the mesopores, 

 which sometimes evidently changed into zooecial tubes, the diaphragms occur 

 regularly seven in 0.5 mm. 



In figs. 4 to 8 on plate XXVII, I have endeavored to represent the principal 

 variations noticed in tangential sections. The most of them are as in fig. 6, and 

 figs. 4 and 5 represent what I regard as a condition of extreme age, differing from the 

 usual condition merely in having an extra internal deposit of hard tissue. Figs. 7 

 and 8, however, deviate in a more important respect in having stronger and more 

 abundant acanthopores. Many of these, furthermore, are developed between the 

 angles, causing an inbending of the tube-walls. The average size of the zooecia 

 in this form, which may receive the provisional name of var. spinulosum, is also a 

 trifle greater than -usual. 



The systematic position of this and the two species following is somewhat 

 doubtful, but after careful reflection I have selected Batostoma as more fitting to 

 receive them than Amplexopora. The closer tabulation of the proximal ends of the 

 tubes, the irregularity of the tubes in the axial region, and their division there (as 

 seen in the central part of transverse sections) into a large and small .series, are 

 characters so far unknown in Amplexopora. But my chief reason for placing the 

 species with Batostoma is found in the marked resemblance exhibited by fig. 8 to 

 similar views of B. implicata and B.jamesi of the Cincinnati rocks. 



Formation and locality. Very abundant in the middle third of the Trenton shales at St. Paul, 

 Minneapolis, and localities in Goodhue and Fillmore counties, Minnesota. 



Mus. Reg. Nos. 5999-6001, 8092, 8095. 



