42 • G. F. MATTHEW: ILLUSTEATIONS OF 



Horizon. This species is first met with iu the dark grey sandstone ot \b, being- among 

 the earliest species which entered the St. John Basin ; at this horizon the variety prima 

 is common in association with Linnarssonia transversa, an Acrotreta, and Lingulella inflata ; a 

 more tumid Acrothele than the variety prima and which may be the typical form of A. 

 Matthewi, is also present. In the upper baud of l.b, which is of a finer texture than the sand- 

 stones of the lower band, var. lata was first found ; and in the conglomerate above it 

 which forms the base of \.c, a form occurs which cannot be distinguished from the type of 

 this species, except that it is not so tumid at the umbo. Professor Hartt's shell was from the 

 shales of l.c ■, above the conglomerate band, and it is in these finer shales and in those of 

 l.d that the typical form of the species is most abundant ; even here, however, (at least in 

 l.c) it occurs in company with a broad form resembling, and probably identical with, 

 var. lata. 



Mr. Walcott compares this species with Acrothele subsidua, White,' from the Cambrian 

 of Utah. It is evidently closely allied to^. granidata, Linnarsson, of the Lower Cambrian 

 of Sweden, but it may be distinguished from that species by its straighter hinge line and 

 greater breadth posteriorly. 



KUTORGINA, Billings. 



KXJTORGINA Latoubensis, u. Sp. (Plate V. Figs. 18, ISa, b, and c.) 



Valves narrowly semi-circular, broader than long, flat ; umbones low ; greatest thick- 

 ness iu the posterior third ; hinge line shorter than the width of the shell. 



Dorsal valve with a distinct median depression extending from the umbo to the front 

 margin, and with low ridges diverging from the beak toward the lateral thirds of the front 

 of the valve. Umbo not elevated above the hinge area, which is exceedingly narrow or 

 absent. Hinge line with two sharp slightly projecting teeth near the umbo. 



Ventral valve with a narrow median ridge extending two thirds of the length of the 

 valve toward the front margin ; also with a fainter ridge on each side diverging towards 

 the lateral third of the border of the valve ; umbo very low ; hinge area perceptible but 

 very narrow, longitudinally striated, and having a minute tooth on each side of the very 

 narrow and small foraminal opening. 



Surface ornamented with about forty or fifty fine, faint, radiating striœ ; those of the 

 middle fifth are close, continuous, and straight ; a few on each side of these are more 

 divergent, while those near the back of the shell are fainter, closer than the last, and 

 moderately arched outward toward the lateral borders. The surface of the valves is also 

 marked by very fine but distinct concentric strine ; and at somewhat regular intervals by 

 about twelve more distinct lines of growth. The concentric strire are usually as distinct 

 as the radiating. Casts of the. interior of the valves exhibit a smooth surface with some 

 irregular, sinuous, radiating striae. 



This shell is rather rare, and is distinguished from the Orthides by its smooth surface. 

 The half-grown shell is about as wide as long. 



The surface ornamentation of this shell is not unlike that of Kuiorgina sculptilis (Meek, 



Exijloration and Survey. West 100 Meridian. Vol. iv. PI. i. p. 34. 



