SPATHELLA. 153 



that up to the present the possession of a periostracum has not been demonstrated 

 in the genus Scaldia, but shells preserved in limestone rarely, if ever, have the 

 periostracum developed, and hitherto Scaldia has only been found in massive 

 limestone. 



Family CCELONOTIDiE, M'Coy. 

 Genus Spathella, Hall, 1885. 



Ctpricaiidia, M'Coy, pars, 1844. Synops. Carb. Foss. Ireland, p. 59. 

 Sanguinolites, M'Coy, pars, 1844. Ibid., p. 49. 



Spathella, Hall, 188-5. Geol. N. York. Palseontol., vol. v, pt. 1, Lamellibranch. 

 II, p. xxxiii. 



Generic Characters. — Shell equivalve, very inequilateral, transversely sub- 

 cylindrical, dorso-ventral diameter longer behind than in front. The anterior 

 end is short, narrow, elliptically curved. Dorsal and ventral margins subparallel, 

 posterior margin truncate or bluntly rounded. Umbones small, anterior. A well 

 marked elongate escutcheon, apparently no lunule. Dorsal slope well defined, 

 hollowed. A well marked constriction in the anterior part of the valve. Ligament 

 apparently external and small. 



Interior. — The anterior adductor muscle-scar small, not bounded posteriorly by 

 a ridge, placed just within the margin of the valve. The posterior adductor scar 

 small, placed immediately beneath the hinge-line and near the posterior margin. 

 Pallia! line entire. Hinge with two small cardinal teeth in the right valve, sub- 

 umbonal, and obsolete lateral teeth. 



Exterior. — Surface adorned with concentric lines and rugas of growth. 



Observations. — The type of this genus is Spathella typica, a shell from the 

 Devonian series of New York. Spathella has a close relationship to Sanguinolites, 

 but is separated by the presence of hinge-teeth, the position of the muscle-scars, 

 the absence of a strong ridge bounding the anterior adductor muscle-scar, and the 

 absence of an angular radiating ridge and of secondary radiating ridges on the 

 dorsal slope. 



Sphenotus, Hall, another Devonian genus, has two cardinal teeth, but in addition 

 there are two slender lateral teeth, and there is always a strong angular ridge 

 crossing the valve from the umbo to the posterior inferior angle, and a secondary 

 radiating median ridge on the dorsal slope, which characters serve to distinguish 

 Sphenotus and Spathella. 



Two species occur in Carboniferous rocks, one being the Oypricardia cylindrica, 



