winTE.] CEETACEOUS. 29S 



Ostrea pellucida Meet & Hayden. 



(Plate L, Figs. 6, 7.) 



This is not the Ostrea pellucida of Defrance 1821, but it is a small 

 species from the Cretaceous of the Upper Missouri Eiver regiou, which 

 was published in Vol. IX of the United States Geological Survey of the 

 Territories, page 15, Plate XXVIII, Figs. 4, a, h. It is probably the 

 form that Dr. Morton supposed to be identical with his 0. falcata ( — 

 0. larva), but it is quite distinct, as was shown by Mr. Meek. It is also 

 evidently the same form that was described by Meek & Hayden under 

 the name of 0. translucida iu the Proceedings of the Academy of Nat- 

 ural Sciences of Philadelphia for 1857, page 147. Both that form and 

 the one they called 0. pellucida are reported from the same formation 

 and same locality, and they are probably identical. A clear specific 

 characterization has not been given of either of the forms ; but in any 

 case the name 0. pellucida cannot hold, because it was used long ago by 

 Defrance for a different species. The latter name is probably an inad- 

 vertent suppositition on the part of the authors for the previously used 

 name 0. translucida. 



Ostrea planovata Shumard. 



Dr. Shumard described this form in the Proceedings of the Boston 

 Society of Natural History, Vol. VIII, page 201. In the same paper 

 both 0. lyoni and 0. owenana were published among other Cretaceous 

 fossils from Texas. As no illustrations of either of these species have 

 been published, and as the type specimens are not accessible, it seems 

 impracticable to identify them among any collections subsequently 

 made. 



Ostrea plumosa Morton. 



(Plate XXXVII, Figs. 5,6.) 

 Dr. Morton obtained this species from the Cretaceous strata of New 

 Jersey, and published it in his Synopsis of the Cretaceous Formation 

 of tbe United States, page 61, Pate III, Fig. 9. It seems to be a very 

 variable form, and the figures here given, although they correctly repre- 

 sent the specimens used, are not very satisfactory. 



Ostrea prudentia White. 



(Plate XL, Figs. 5, 6.) 

 The only specimens of 0. prudentia that have yet been discovered 

 were obtained irom the Cretaceous strata of Southern Utah. It was 

 originally published in the reports of the United States Explorations 

 and Surveys West of the 100th Meridian, Vol. IV, page 171, Plate XIV, 

 Figs. 2, ff, h, c, d. 



Ostrea qiiadriplicata Shumard. 



(Plate XLIII, Figs. 5, 6, 7.) 

 Under the entry of Ostrea crenulimargo on a previous page it has 

 already been stated that the form bearing that name is believed to be 



