434 PALEONTOLOGY OF ILLINOIS. 



for placing; this species under Batostomella. This peculiar struc- 

 ture is present in well preserved examples of B. gracilis James, 

 as figured on plate XXXV, fig. 2. 



Position and locality: Hamilton group, Alpena, Michigan. 

 The specimens from which this description is drawn were kindly 

 donated to the author by the Rev. W. H. Barris, of Davenport, 

 Iowa. 



BATOSTOMELLA INTERSTINCTA Ulrich. 



PI. LXXV, fig. 4-4c. 



Zoarium forming a very thin incrustation, spread upon crinoid 

 columns, throwing up irregularly branched shoots, one mm. 

 or thereabouts in diameter at the basal portion, and somewhat 

 more higher up. Surface smooth; when well preserved hirsute. 

 Zooecial tubes make a very abrupt bend from the axial to the 

 peripheral region. Apertures varying from circular to oval, 

 about nine in two mm., measuring along the irregular obliquely 

 ascending intersecting rows of apertures. In the thin basal ex- 

 pansion the interspaces are less wide, and there are fewer meso- 

 pores. Here the average long diameter of the oval apertures is 

 about 0.18 ram., while upon the ramose portion the diameter 

 of the mostly circular apertures rarely exceeds 0.1 mm. A 

 considerable number of mesopores are developed upon the ra- 

 mose portion. Diaphragms few or wanting. The cortical re- 

 gion is equal in thickness to about the diameter of the axial 

 region, the most marked peculiarity of this species and one 

 which at once distinguishes it from all other species of the genus. 



The irregular growth, large basal expansion, and its larger 

 cell apertures, readily distinguish this species from B. spinulosa. 



Position and locality: St. Louis group; rather rare at Pella, 

 Iowa. 



BATOSTOMELLA SPINULOSA Ulrich. 



PI. LXXV, fig. 1-le. 



Zoarium slender, ramose, branching at greater or less inter- 

 vals, the cylindrical stems from one to two mm. in diameter. 

 Surface smooth; when well preserved, hirsute. Zooecial tubes 

 thick-walled and direct in the cortical region after making a 

 rather abrupt turn from the axial region where they are thin- 



