I. \MKM.I l;i:\M H1\TA .'. I .'. 



modtollformJ. 1 



The systematic posit i<>n of Artinomyn seems to be nearly intermediate between 

 Orthodesmn ami .l/f//<i//i.-/x. <litlerinK from the former in the somewhat shorter form 

 an. I tightly dosing instead of gaping valv.->. from the latter in the thinner hinge 

 plate aii'L-h.-il. ami from l.otli in tin- <-oii\.-x basal outline and absence of a mesial 



ATI!fOMYH MoI'lol.lKoKMI-. M.. .,,ii II .,-'/, 



II \TE XXXVI. HOB. 10 .od 



modioliformu MKBK and WOHTIIKX, 1888. Oeol. Sur. III., vol. Ill, p. 204. 

 Compare Jfoftoioprfi tujvrba HALL, 1881. Bep't,, Sup't. Oeol. Sur. WIs., p. 31. 



Shell of im-liiim size, elongate, obliquely ovate, much the widest in the posterior 

 half; strongly convex. Hinge nearly straight, rather short, extending anterior to 

 tin- l.i-.ik- almost half as far us posterior to them, and posteriorly less than half the 

 <li-tamv from the l.rak-; to the posterior extremity of the shell. From the hinge 

 tin- outline passes almost imperceptibly into the oblique posterior margin, and tin- 

 slopes backward with a gentle convexity to the abruptly rounded posterior basal 

 extremity. Masai margin extending obliquely upward and forward, very slightly 



convex throughout its length. Anterior end narrow, rounding sharply into the 







extremity of the hinge. Beaks rather prominent, incurved, situated about one-sixth 

 of the entire length of the shell from the anterior extremity; a strongly rounded or 

 subangular umbonal ridge extends from the beaks to the posterior extremity of the 

 shell, the convexity becoming gradually less as it recedes from the beaks. Surface 

 with fine concentric -t ri.i- and rather strong (especially on the flattened regions 

 anterior to the umbonal ridge) wrinkles of growth. Muscular impressions so faint 

 that they cannot be traced with certainty on the casts of the interior at hand. 



I believed this species to be identical with Hall's previously described Modio- 

 lopsis superba, but Prof. If. 15. \V bitfield, to whom a specimen was sent for compari- 

 son with the original types of Hall's species, writes me that it is "less angular on 

 the umbonal ridge, more rounded on the base, and fuller on the lower disc." These 

 litlerences are i>rol>al>ly <>f >|>ecific importance. Figure 20 is taken from the type 

 used by Meek and Worthen. The specimen, though a good one, is slightly distorted 

 by vertical pressure, and imperfect in front and along the base. To facilitate com- 

 parison with ti^r. I'.i. the missing parts have been restored in the figure. 

 This fine species I regard as in every sense an Aifinmnya. It is, \tcr\ 

 ffordi Ulrich. than any other known. Imt there is little likelihood of confusion 

 between them, that species being a higher shell, with a larger anterior eml ami 

 somewhat smaller umboncs. It has also several ra<liatit,- fN- on the posterior 

 cardinal slope not seen in this species. 



