﻿44 SMITHSONIAN MISCELLANEOUS COLLECTIONS [VOL. 47 



progenitors. It is only in this way that we may hope to establish 

 their genetic relations to the Ordovician types. 



The genotype, M. cequalis, has given us much trouble. While the 

 apparently total absence of acanthopores in the specimen from which 

 the original figured set of thin sections was prepared, has been veri- 

 fied bv another set of sections from the same, the lamentable fact 

 remains that none of the numerous specimens hitherto believed to be 

 of the same species is without them. After many failures to identify 

 another specimen of the species, we have been forced to the convic- 

 tion that the original type is unique. If it is not, then the specimen 

 illustrates a wholly unparalleled abnormal condition of either pres- 

 ervation or structure. A fact opposed to the latter alternatives was 

 brought out by a final comparison of the specimens involved in the 

 question at issue, viz : of the hundreds of specimens of the new Ani- 

 plexopora which, prior to our recent investigations, had been labeled 

 as .1/. cequalis, not one had such broad monticules as the type speci- 

 men. Indeed, they cover as much or more space, and this despite the 

 fact that they are lower than in any other type of Trepostomata 

 known to us. The only species approaching or possibly equaling 

 it in this respect is Discotrypa elegans. Difference merely in the 

 height of monticules is usually of very little consequence, but the 

 widening of their bases seems to indicate a structural difference, the 

 interpretation of which involves the difficult question of the purposes 

 of the " maculae " themselves. 



On account of the extreme rarity of the genotype, Monotrypella 

 has been known to collectors only through the M. quadrata section 

 of the genus. As the latter section constitutes a sharply defined 

 natural group and deserves recognition as a distinct genus, we have 

 decided to remove it under the following title and to allow Mono- 

 trypella either to stand or to fall with the species upon which it was 

 originally based. 



Genus Rhombotrypa new genus 



Generic diagnosis. — Ramose Amplexoporidce with zocecial tubes 

 in axial region regularly quadrate or rhombic in cross-section. Acan- 

 thopores usually wanting, always shallow, rarely distinguishable 

 internally. True mesopore absent, but wall-less tabulated inter- 

 zocecial spaces occur in several of the species. 



Genotype. — Monotrypella quadrata (Rominger). a very abun- 

 dant and one of the most characteristic and widely distributed fossils 

 of the Richmond formation. 



This group of species was recognized by Ulrich in 1890 * when 



1 ///. (,Y<>/. Surv., vol. viii. pp. ?,jj, 45_'. 



