SPECHTS FERRY BRYOZOAN FAUNA 33 



specimens) seven entire zooecia, or seven complete zooecia and part of eighth, 

 in 2 mm, measuring as closely as possible parallel to direction of elongation of 

 zooecial apertures; less commonly (154 of 382 measurements on 39 specimens) six 

 complete zooecia or six entire zooecia and part of seventh in this distance; maxi- 

 mum diameter of zooecial aperture averages 0.21 mm (404 measurements on 39 

 specimens); average interapertural zooecial wall thickness (522 measurements on 

 39 specimens) is 0.11 mm; zooecial wall material commonly consisting of fine 

 laminae concentrically disposed about zooecial apertures; divisional line between 

 adjoining zooecia commonly prominent, dark- or light-colored, but in some speci- 

 mens locally obscure; cingulum-like structures associated with many zooecial aper- 

 tures. Mesopores thick-walled, angular or subangular, generally with round or 

 ovate apertures that commonly are strikingly smaller than mesopores because of 

 thickness of mesopore wall material; mesopores aggregated into maculae, else- 

 where sparse to common; in some specimens, mesopores common in some areas 

 but virtually absent elsewhere. 



Longitudinal section. — Mesotheca thin, somewhat flexuous, and apparently 

 lacking tubuli or foramina. Zooecia usually somewhat prostrate and thin-walled in 

 earliest development but rapidly becoming erect and very thick-walled; zooecial 

 wall material of conspicuously developed A-shaped laminae; divisional line between 

 contiguous zooecia commonly observed. Diaphragms lacking. 



Remarks. — From 404 measurements on 39 specimens, the maximum apertural 

 diameter of the zooecia, exclusive of the zooecial walls, averages 0.21 mm. The 

 average for different specimens does not deviate from 0.21 mm by more than 0.04 

 mm; and this for only one specimen on which ten apertures were measured. The 

 average interapertural zooecial wall thickness, based on 522 measurements on 39 

 specimens, is 0.11 mm. For any particular specimen, the average value of this 

 dimension is not greater than 0.15 or less than 0.08 mm. Text figure 4 shows 

 measurements of maximum apertural diameter of the zooecia, interapertural zooecial 

 wall thickness, and number of zooecia in 2 mm. 



Spechts Ferry representatives of this species show considerable variation 

 in number of mesopores. Such variation is displayed not only from specimen to 

 specimen but also within different areas of the same zoarium. Mesopores are so 

 scarce in some parts of the colony that locally a marked similarity is shown in 

 tangential section to Stictoporella angularis Ulrich, a species characterized by its 

 paucity of mesopores (Ulrich, 1895, pi. XI, fig. 8) and ribbonlike branches that 

 are 1.5 to 3.0 mm wide; elsewhere, in the same zoarium, mesopores are consider- 

 ably more plentiful as in S. frondifera (Ulrich, 1895, pi. XI, fig. 16). None of the 

 Spechts Ferry specimens identified as 5". frondifera approach S. angularis in zoarial 

 form, but some have noticeably fewer mesopores than in S. frondifera as figured 

 by Ulrich; some may recommend assignment of these latter specimens to S. angularis 

 var. intermedia, which Ulrich (1895, p. 183) regarded as occupying an intermediate 

 position between S. angularis and S. frondifera . The writer feels that S. angularis, 

 S. angularis var. intermedia, and S. frondifera possibly may have been members 

 of a single natural population. 



The divisional line between adjoining zooecia may be observed throughout 

 the entire tangential section of some specimens, as is depicted by Ulrich (1895, 

 pi. XI, fig. 16), but in other specimens this line is prominent locally although 

 obscure or not observed in other areas. I felt that the prominence of development 

 of this divisional line may be related to depth of sectioning; tangential sections, 

 however, prepared at different levels or depths within the zoarium, indicated such 

 is not the case. 



