Vol. 34, pp. 147-148 August 29, 1921 



PROCEEDINGS 



OF THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



A 



AMECYSTIS, A NEW GENUS OF ORDOVICIAN 



CYSTIDEA.i 



BY E. O. ULRICH AND EDWIN KIRK. 



In a recent publication Raymond^ described a new species 

 of Cystid under the name Pleurocystites laevis. This species 

 he states is chiefly remarkable in that it lacks pectinirhombs 

 and surface sculpture. The absence of pectinirhombs is not 

 an abnormality or due to weathering. The species is referable 

 to a new genus, for which we propose the name Amecystis 

 (Sjurj, a shovel), with Pleurocystis laevis Raymond^ as the 

 genotype. Two other species belonging to the genus are known 

 which diverge somewhat from the type species but agree in 

 gross structure and in the absence of rhombs. 



Amecystis may best be defined as a Pleurocystis lacking 

 pectinirhombs. The evidence is perfectly clear on this point. 

 A large number of specimens in a splendid state of preservation 

 have been examined, and in none is there a trace of rhomb 

 structure. Even in the one species known that has radiating 

 surface ridges, the ridges appear rather as superficial ornamen- 

 tation than as stereom folds. The arrangement of plates is as 

 in Pleurocystis. The anal side is nearly always poorly preserved 

 owing to the fact that it is made up of very small plates and is less 

 rigid than in Pleurocystis. The anal pyramid has doubtfully 

 been determined as having the same position as in Pleurocystis. 



Amecystis laevis (Raymond) or a very closely related species 

 also occurs in the Curdsville limestone of Mercer County, 



1 Published by permission of the Director of the U. S. Geological Survey. 



2Raymond, P. E.. "A contribution to the description of the fauna of the Trenton 

 Group:" Canada Dept. Mines. Geol. Survey Mus. Bull. No. 31, Geol. Ser. No. ,3S, Feb., 

 1921. 



aOp. cit., p. 2, PI. II, figs. 1-3. 



20— Proc. Biol. See. Wash., Vol. 34, 1021. (147) 



