78 The Ottawa Naturalist [October 



position, and outline ustially is absent among those thecal 

 plates not bordering on the transverse apical food-groove or 

 on the anal pyramid. However, certain tendencies may be 

 observed even among these other thecal plates. For instance, 

 the plate directly below the middle of the anal pyramid (Plate 

 II, fig. 2 ; also text diagrams), but not in contact with the latter, 

 is pentagonal in form, and has its upper angle inserted between 

 the two plates forming the lower border of the pyramid. 

 Directly beneath this pentagonal plate is a series of hexagonal 

 plates which, instead of forming a strictly vertical row, are 

 arranged along a line which curves moderately toward the 

 front on approaching the base of the theca. Parallel to this 

 series of plates, on its anterior side, are similar series of hexa- 



Anierior stda 



A*js of 



Foo*d- 

 Groove 



Posterior side 



Text figure No. 3. The two lower series of thecal plates of the specimen represen- 

 ted by text figure No. 2, and by figure 2 on plate II ; drawn as though viewed from 

 the lower side and oriented as indicated in the diagram. The vertical projection 

 of the plane passing through the anal pyramid and parallel to the transverse apical 

 food-groove is indicated by the dotted line. The dotted parts surrounding the 

 top of the column indicate the extent to which the basal part of the lowest series 

 of plates rises above a line drawn strictly horizontal around the top of the column. 

 The dotted area at the center represents the lumen. Fifteen plates occur in the 

 basal series of thecal plates in the specimen diagrammed, but the number varies 

 greatly in different specimens. 



gonal plates, causing the anterior side of the theca to present 

 the appearance of diagonally intersecting rows, with the angles 

 of the thecal plates directed toward the top of the specimen. 

 On the posterior side of the theca, a similar tendency toward 

 the arrangement of plates in rows causes one of the sides of the 

 hexagonal plates, rather than one of its angles, to face the top 

 of the specimen. 



12. The arrangement of the basal thecal plates. The outline 

 and arrangement of the basal thecal plates, where in contact 

 with the stem or column, varies from 11 to 15 (Text diagram 

 No. 3) in different specimens. The line of contact between the 

 basal thecal plates and the top of the column is not strictly 

 horizontal, but rises and falls in an irregular manner, varying 



