NO. 5 ORDOVICIAN BRYOZOA — BOARDMAN 1 9 



(Ulrich, 1893, p. 295) and is here reassigned to Amplexopora, the 

 original genus. 



The available evidence strongly indicates that two types of 

 acanthopores are present in the type species and in most of the other 

 Upper Ordovician species of Amplexopora. In the type species, the 

 shorter, offset acanthopores generally are concentrated in early and 

 middle parts of exozones and largely between zooecial comers, in 

 contrast to the long acanthopores extending throughout the exozones 

 and centered in zooecial corners. In tangential sections, the total 

 number of acanthopores in areas containing offset acanthopores is 

 approximately twice that of areas without offset acanthopores. 



Some of the short offset acanthopores appear almost spinelike. 

 In tangential sections acanthopores are cut transversely and offset 

 acanthopores always have an extension of skeletal material con- 

 necting the acanthopores and zooecial walls. Thus, regardless of the 

 first impression given in plate 5, figure 2e, offset acanthopores in three 

 dimensions are not spines supported only at their bases and projecting 

 freely into the zooecial voids, but "spines" supported continuously 

 along their lengths by a ridge of skeletal material connected to zooecial 

 walls. 



A distinction is made between inflection of zooecial walls by off- 

 set acanthopores and inflection of zooecial walls by acanthopores rela- 

 tively large in diameter and centered on zooecial boundaries. Ex- 

 amples of inflection by large, centered acanthopores are found in 

 Amplexopora conferta (Coryell) and A. winchelli var. spinidosum 

 (Ulrich), both Middle Ordovician forms. 



The taxonomic significance of the offset acanthopores cannot be 

 estimated until much more is known of the distribution of related 

 species and their morphologic variation. Offset acanthopores are not 

 now considered a necessary attribute for the genus Amplexopora, 

 or a basis for erection of subgenera within the genus. 



The genus Acanthotrypella Vinassa de Regny was described merely 

 as a thick-walled Acanthotrypa and the originally designated type 

 species is Batostoma variabile Ulrich, 1890. The cotypes of B. 

 variahile are in the U. S. National Museum collections and consist of 

 four partly silicified specimens from the top of the Richmond group, 

 Osgood, Ind. The cotype originally figured by Ulrich (i8go, pi. 35, 

 fig. 5) is here designated the lectotype (U.S.N.M. 43820) and sec- 

 tions are illustrated on plate 7, figure i. The specimen does not seem 

 to differ significantly from Amplexopora septosa, except for the lack 

 of offset acanthopores that inflect zooecial walls. The species is here 



