BRYOZOA. 421 



tures. Peristome faint. Interspaces occupied by very thin- 

 walled, angular mesopores, which are sometimes open at the 

 surface. When this is the case, the surface resembles that of 

 some species of Callopora. From four to seven diaphragms are 

 developed in the zooecial tubes as they leave the axial region. 

 Diaphragms numerous in the mesopores. Acanthopores small 

 and usually inconspicuous, often projecting a little into the 

 zooecial cavity owing to the thinness of the walls. 



The characters of this species are so distinct from T. debilis 

 with which it is associated, and from other species of the genus 

 that comparisons are unnecessary. Its surface bears some re- 

 semblance to certain species of Callopora, but the internal struc- 

 ture is widely different. 



Position and locality: Cincinnati group, Alexander County, 

 Illinois. 



NICHOLSONELLA Ulrich. 



(For generic rliagnosis see page 374.) 



Only four or five species are known having the peculiar 

 characters upon which this genus is founded. Two of these, N. 

 ponderosa, the type of the genus, and an undescribed species, 

 are from the Trenton limestone, the other two or three from 

 the Cincinnati group. Of the latter, N. vaupeli was described by 

 me as a species of Heterotzypa* It is not uncommon near 

 the tops of the hills at Cincinnati, Ohio. A closely allied species 

 or variety occurs about 250 feet higher in the series and is 

 bundant at several localities in Ohio. The fourth form is 

 described here for the first time. It also belongs to the Cin- 

 cinnati group, but is not yet known from any other locality 

 than Wilmington, 111. 



The affinities of Nicholsonella, are with Constellaria Dana, but 

 the absence of stellate maculae, is quite sufficient to distinguish 

 them. The frondescent species resemble Heterotrypa Nich., but 

 the relationship is much more remote than I at one time 

 thought. 



The generic name is given in honor of Dr. H. Alleyne Nichol- 

 son, as a slight token of my appreciation of the great value of 



*Jour. Cin. Soc. Nat. Hist., voL VI, p. 85. 



