442 THE PALEONTOLOGY OF MINNESOTA. 



[Orlhis (Dalrnanrlla) testudinarin . 



Original description: "0. testa confertissime striata, costis subalternis eleva- 

 tioribus; valva minor! subplana semiorbiculari; majori basi gibba, nate prominula 

 nutante. Locus. Ostrogothia ad Borenshult, in calce cinera. Longit. 15 mm., 

 latit. testa? 15, lat. valvte minoris ad basin 12 mm., crass, 7 mm. 



"Species quasi media inter 0. eleyantulam et 0. basalem, ad utraque distincta 

 ambitu magis orbiculari, mini me ad cordatum tendente, praesertim vero costarum 

 radiantium ratione, quae enim duplicis sunt generis, videlicet; elevatiores (circiter 30), 

 testse basin fere attingentes; et humiliores plus minus abbreviate, quarum 2-3, inter 

 par priorum. 



" Valva minor subplana, 1, in medio longitudina liter subimpressa; suborbicu- 

 laris, basi truncata, apice vero rotundato, minime prominulo. Linea cardinalis quam 

 valvae longitude manifesto brevior. Valva major basi gibba, nate prominula, modice 

 curva valvae minoris convexitatem minime attingente. Subnate areola triangularis 

 impresso-plana, foramine deltoideo brevi. 



"Obs. Rostrum quam in 0. elegantula minus sed quam in 0. basalis magis curv- 

 tum; margo cardinalis quam in utraque specie brevior. Specimina plura consulti 

 similia." 



The following description of 0. emacerata Meek (not Hall)-=0. testudinaria, var. 

 meeki Miller, is given, as it applies to this species in all of its details, except that the 

 former is larger and more robust than in the majority of specimens usually referred 

 to 0. testudinaria: "Species small, plano-convex, rather depressed, transversely 

 truncato-suboval, the length being about five-sixths its breadth [sometimes as wide 

 'as long]; hinge-line perhaps always a little shorter than the greatest breadth of the 

 valves; lateral margins generally rounding to the hinge, most prominent at, or a 

 little behind the middle, and rounding to the front, which is usually somewhat 

 straightened, or very faintly sinuous, at the middle; or presents a regular semi- 

 circular outline. 



"Dorsal valve nearly flat, or slightly convex on each side of a shallow mesial 

 sinus, that commences very narrow at the beak and usually widens rather rapidly 

 to the front; beak very small, scarcely projecting beyond the edge of the area, and 

 not incurved; area low at the middle and narrowing off to nothing at the lateral 

 extremities of the hinge, slightly arched, and directed obliquely backward; foramen 

 [delthyrium] very small and filled by the [large trilobed, striated] cardinal process. 

 Interior very shallow and provided with a slender mesial ridge that extends about 

 halfway forward from the hinge, between the muscular impressions, which are not 

 usually well defined; scars of posterior pair of adductor muscles smaller and usually 

 deeper than the anterior and situated close back under the brachial processes; those 

 of the anterior pair three or four times the size of the posterior [commonly not more 



