I. \Ml.l. I. II i: \\< MIATA 



M. . . .-: , 



umhones loss tuiiiiil ami not - n prominent. Tin- inr 



meiit s,,j, | l(M t, alsn are very much less distinct. II MI oblique. 



shorter ami lias a longer hinge ami narrower escutcl ..... n. 



i.( ;. r.j.'i.';/ t; Mlnne<)U. 



.r.. X.ttd. 



101 I'l.rril'H \|;|i|.\. llnch. 

 I'lethocanlia, I Mm i l.iin., p. 243. 



il thiii. inequilateral, oblique. tumid. with margins dosed; I teaks large, 



:iiniMit. spirally enrolled ami eurviii'' forward. l'.i-:i-nor cardinal margin \\itli 

 a narrow escutcheon or lunette. A strong and larjre process projects forward and 

 downward from the underside of the liin-r ju-t l.eneath the ln-ak in each valve; one 

 strong linear lateral tooth, or thickened internal cartilage -npport. l.eneath the 

 posterior extremity of the hin^e line and rinse to the margin. Anterior muscular 

 scar strongly impressed, situated in the antero-loral an^le, margined on the inner 

 side l-y a cnrvrd ridge extending from the under side of the cardinal process. In 

 casts of the interior the tilling of the anterior impn'-ion- form- a small but sharply 

 defined l..l>e. I'o-terior inu-ciilar -car- indistinct, much larger than the anterior. 

 situated just l>ehind the 01 f the postero-cardinul slope. I'allial line -implc. 



sulinuirginal, faintly itnpre>sed. 



Type: /'. nmbnatn I'lrich. 



In the original description of this genu- and of the typical species, I called the 

 suhrostral [irocess a cardinal tooth. This view I now believe to be at variance with 

 the facts, fur the reason that the supposed tooth does not project beyond the plane 

 of the margin- of the valve and therefore could not have interlocked with a corres- 

 ponding tooth or teeth in the opposite vahr. In the left valve, upon which the 

 genus am! /'. unilmn'ilii rocess was somewhat injured in c 



in- away the adhering matrix. It is, however, sutliciently preserved to show that 

 it had one large tr.i depression in the lower part (for which reason it was 



described as hitid) ami probably one or two in the upper part. In an imperfect ri^'ht 

 valve, recently obtained from Kentucky, the process is similarly marked with a large 

 depression in the lower part and two (perhap- tln.-e) smaller prominences al" 

 In neither specimen are the upper prominences in a sutiiciently good state of pres- 

 enation to admit of po-it .mit ions respecting their character and purpose. 



Still it i> reasonable to suppose that they represent hinge te 



those of \Vhitrlln. especially -h: \vithinthelineofthe hinge. A-tothe 



lower part of the process, why should it i. -upported a" internal cartilage? 



