ulrich-bassler] revision of paleozoic bryozoa 287 



in clusters .of four to eight, with chisters of four or five occurring 

 oftener than six to eight. Connecting threads about 0.03 mm. in 

 thickness, comparatively straight, with clusters of vesicles occurring 

 at intervals of 2.5 mm. or more. 



Compared with A. stcUatum, this species is distinguished by its 

 usually fewer and less closely arranged vesicles in each cluster, by 

 the greater average length and more pyriform shape of the vesicles, 

 and by the comparative rigidity of the connecting threads. 



Occurrence. — Wenlock shale, Buildwas beds, Shropshire, Eng- 

 land ; Rochester shale, Lockport, New York ; Waldron shale, Wal- 

 dron, Indiana. 



Cat. Nos. 43,135, 43,138, U. S. N. M. 



ASCODICTYON STELLATUM Nicholson and Etheridge, Jr. 



(Plate LXVIII, 9, 10) 



1877. Ascodictyon stellatuni Nicholson and Etheridge, Jr., Ann. & Mag. 

 Nat. Hist., ser. 4, xix, p. 464, pi. 19, figs. 1-6. 



1891. Ascodictyon stellatuni Whiteaves, Contr. Canadian Pal., i, p. 213. 



1892. Ascodictyon stellatuni Vine, Proc. Yorkshire Geol. & Polyt. Soc, 

 XIX, p. 89. 



1893. Ascodictyon stellatuni Ulrich, Geol. Minnesota, in, p. 113, fig. 8a. 

 1897. Ascodictyum stellatuni Simpson, Fourteenth Ann. Rep. State Geol. 



N. Y. for 1894, p. 603, fig. 220. 

 Not Ascodictyon stellatuni Vine, 1881 (= Ascodictyon siluriense Vine). 



Original description. — " Colony composed of ovoid or pyriform 

 calcareous vesicles, varying in length from one fifth to one third of a 

 line, and usually disposed in stellate clusters, each containing from 

 three to six cells, or sometimes more. The walls of the vesicles are 

 perforated by microscopic foramina, usually showing a distinctly 

 linear arrangement. The clusters are connected together by creep- 

 ing filamentous tubes, the free surfaces of which are perforated by a 

 single row of minute foramina, and which generally anastomose so as 

 to form a network." 



This common and widely distributed species maintains its specific 

 characters with great constancy. Still, it agrees too closely with cer- 

 tain specimens of A. siluriense to render their separation always easy. 

 As a rule the Silurian species has fewer vesicles in its clusters, and 

 these generally occur also at longer intervals. Again the inner ends 

 of the vesicles are never drawn out in A. stellatmn as is common in 

 A. siluriense. Finally, in a close comparison, the connecting threads 

 impress one as being less rigid in the Devonian species than in the 

 older form. 



