BRYOZOA. 



351 



with which the tangential section necessarily passes through 

 the somewhat laterally directed cells. This is shown in Poly- 

 porn, where the inflections on each side are about equal in the 

 central row or rows of cells, while in those of the marginal rows, 

 which are directed laterally, they appear unequal as in Fene- 

 stelki and other genera having only two ranges of zooecia (see 

 PI. LY. fig. 4). The superior hemiseptum, to which these inflec- 

 tions are due, forms a ridge-like thickening on the inner side 

 of the cell, which becomes obsolete, or nearly so, toward the 

 center of the posterior side of the primary aperture, and en- 

 tirely so at about the middle of the vertical sides, being strong- 

 est in the region of the angle, formed by the union of the lat- 

 eral walls and the slightly convex front or top of the cell. The 

 accompanying digrams will probably serve better to show the 

 peculiarities in question than any verbal explanation. 



This peculiar feature 

 (whose functions unless 

 it acted as a support to 

 the cell front, is unknown) 

 was noticed in 1878 by 

 Mr. A. W. Waters and 

 described and figured by 

 him in the transactions 

 of the Manchester Geol. 



Fig. 10. Diagrams illustrating the different ap- ^OC. for that year, also 



pearances presented in thin sections by the zoce- |)y ^{ r John Young who 



cium of a Fenestellid having both hemisepta. a and .,*,, r< i a 



b. side and end sectional views of the zooecium crossed in the Trans, (reol. SoC. 



by five dotted lines, a, b, c, d and e. Drawings a", b", * fMasoY\tr fr>r- 1 7Q 



c", d" and e" represent the zocecial cavity as it ap- ( ' y ' 



pears in tangential sections at levels corresponding gives a short description 



to the dotted lines, c, represents a "nest" of the , . ,, . 



outlines. f ^- The former found 



two identations but the latter failed to notice that the appar- 

 ent inflection on the one side of the cell of species of Fenestella 

 is caused by the slight lateral direction of these walls in such 

 form.* 



d' 



* In this connection it seems proper to show how imperfect observations of certain 

 defective specimens have led the Messrs. Young and Young into an error, which ap- 

 pears not only to have been overlooked by Mr. Vine, but induced him to propose a new 

 family for the sub-generic division proposed by those authors. In 1875 they publif l:ed a 



