716 CAMBIUA N an A (HIorODA—WALCOTT. 



that the area was somewhat simihir to tlie :irea of that species. The 

 cast of the inti'rior of the ventral valve shows a rather long, large 

 foramen, in advance of which two ridges (vascular trunks) diverge 

 sonunvhat, as in the ventral valve of 1'. inonieri. There is also jjresent 

 a sliort longitudinal dei)ression in the cast, which indicates a corre- 

 sponding mesial ridge just in advance of the foramen. The surfoce of 

 the interior of the shell is marked by fine concentric lines and very 

 fiue interior ridges. Shell substance apparently corneous. 



This species is founded upon two semic^asts of the ventral valve, 

 preserved in comi>aet gray limestone. The shell appears to be verj' 

 thin over the outer iiortions and tliiek over the umboual region. 



The generic reference is somewhat doubtful, owing to the close 

 generic relations of Yorlia, AcrotheJe, and Discinopsin. The foramen 

 and form of the vas<'nlar trunks suggest Yorlia, while the shell 

 substance and surface characters arc more those of Aeroihclc. 



Formation and loeaJiti/. — Lower Cambrian, one-fourth mile east of 

 Salem, Washington County, New York. (Xo. 2G434, T\S.N.IV[.) 



ACROTHELE DECIPIENS, new species. 

 (Plato LX, fij.-. 2.) 



General form of the ventral (pedicle) valve nearly circular, the length 

 and breadth being nearly the same; moderately convex, most elevated 

 at the apex, which is truncated by a rather large foraminal opening. 

 Cardinal slopes rounded, forming an obscure false area on each side of 

 the flattened pseudodeltidium, which appears to have a slight groove 

 down its center. Surface marked by fine concentric stria' and lines of 

 growth, which pass around back over the area and pseudodeltidium. 

 Shell substance corneous, or it may be j^hosphatic. The shell has the 

 same appearance as AcrotheJe and Linnarssonia. 



Only one specimen of this shell was found associated with Linnars- 

 sonia and fragments of OleneUns, in a fine gray limestone interbedded 

 in the Lower Cambrian shale. It resembles quite strongly the ventral 

 valve of I)iscino2)sis fjidielnii, IMatthew, illustrated by Hall and Clarke.' 

 It difiers, however, in the presence of an obscure pseudodeltidium, and 

 for the present I prefer to j)lace it with Aerotlieic until more is known 

 of the genus J)iscmo2)sis. 



Formation and h>C((Jity. — Lower Cambrian, York Terrane^, !>!, miles 

 north of Stoner's Stati(m, York and Wriglitsville llailroad, York 

 County, Pennsylvania. (No. 26435, T.S.N.M.) 



ACROTHELE BELLULA, new species. 

 HMateLX, figs. 4, 4a-4e.) 



General form of valves subcircular, moderately convex. Ventral 

 (pedicle) valve highest at the apex and perforated by a circular fora- 

 men, in front of which there are two small, sliort, sharp spines. The 



I ]'al. X. v., VIII. I't. I, 1,S1L\ 1.1. Ill, W' 



