124 



BULLETIlsr 77, UNITED STATES NATIONAL MUSEUM. 



and more complete specimens preserving the pointed base are by no 

 means rare. Although Eichwald gives but a single illustration of the 

 species, a view, natural size, of a zoarium preserving the pointed base 

 (fig. 49 a) , there can be little question that his type of Coscinium 

 proavus and the specimen figured in the present work are identical, 

 mainly because Graptodictya proava is the only known cribrose Mid- 

 dle Ordovician Russian bryozoan with the pointed base and dimen- 

 sions shown in his figure. This same species has been found in 

 American strata, as determined from my study of the specimen (see 

 fig. 6, pi. 9) which Sardeson, in his ' 'Problem of the Monticuli- 

 poroidea"^ figures and describes at length under the name of Stic- 

 toporella cribrosa Ulrich. In spite of Sardeson' s statement to the 

 contrary, it is a fact that species of Stidoporella have an expanded 

 incrusting base and never have a pointed base for articulation. Com- 

 parison of figures of 

 both species here pre- 

 sented can not fail to 

 convince the discrimi- 

 nating person of numer- 

 ous zoarial and zooecial 

 differences between 

 Stictoporella crilrosa 

 Ulrich and Graptodictya 

 proava. Indeed, ob- 

 servers who have had 

 opportunity to study 

 numerous examples of 

 these several types of 

 structure, assign them 

 to separate families, as 

 in the present work. Graptodictya proava is known from a second 

 American locahty, namely, along the Escanaba River in Mchigan, 

 below the upper falls. A fine, large example from this place was 

 made the type of Hall's ClatJiroporaflaheTlata. Through the courtesy 

 of Dr. E. O. Hovey, of the American Museum of Natural History, I 

 have had the opportunity of studying this type and of presenting 

 an illustration of its minute structure to show the specific identity. 

 The specimen itself has been broken out of the sohd limestone and 

 thus is parted along the mesial lamina. Its cribrose zoarium has 

 the same dimensions seen in the large examples of G. proava, and it 

 clearly arises from a pointed base, although a portion of this is 

 broken away. 



The cribrose, bifoliate bryozoan, figured by Billings as Coscinium 

 'proavus Eichwald, may be correctly identified, but in the absence of 



Fig. 49. — Graptodictya proava. a, Eichwald's view of the 



TYPE-SPECIMEN" OF HIS COSCINIUM PROAVXIM, NATURAL SIZE, 

 SHOWING THE CRIBROSE ZOARIUM AND THE CHARACTERISTIC 

 STRIATED, POINTED BASE. " CALCAIRE A 0RTH0CERATITES,"NEAR 



Reval, Esthonia; 6, tangential section of Hall's type of 



ClATHROPORA FLABELLATA, X30, INTRODUCED FOR COMPARISON. 



Lowest Trenton, Escanaba River, Michigan. 



1 Jounu Geol,, voL 9, 1901, p. ISO. 



