CAMBRIAN BRACHIOrODA: GENERA IPHIDEA AND 

 YORKIA, WITH DESCRIPTIONS OF NEW SPECIES 

 OF EACH, AND OF THE GENUS ACROTHELE. 



By Charles D. Walcott, 



Honorary Curator, Department of Invertebrate Palaontology. 



This is the tirst of a proposed series of preliminary papers ou the 

 Cambrian iBracliiopoda, to be published in advance of a memoir on the 

 subject. Owing to administrative duties, only a small part of each year 

 can be devoted by me to pala'ontologic studies. In the present paper 

 the genera Iphidea and YorVm are discussed. Succeeding papers will 

 treat of other well-known genera. 



IPHIDEA, Billings. 



Iphidea, Billings, 1872, Cau. Nat., new ser., VI, p. 477, tig. 13. 



Mtcromitra, Meek, 1873, Sixth Ann. Kept. U. S. Geol. Surv. Terr., for 1872, p. 47!1. 



Iphidea, Billings, 1874, Pal. Foss., II, Pt. 1, p. 76. 



Iphidea, Linnarsson, 1876, Bihang Till K. Svenska Vet. Akad., Haudliugar, 



No. 12, p. 26. Brachiopoda of the Paradoxides Beds of Sweden. 

 Iphidea, Walcott, 1886, Bull. U. S. Geol. Surv., No. 30, p. 100. 

 Paterina, Beechek, 1891, Am. Jour. Sci., XLI, p. 345. 

 Iphidea, Hall and Clarke, 1892, Pal. N. Y., VIII, Pt. 1, p. 97. 

 Iphidea, Hall aud Clarke, 1892, Eleventh Ann. Kept. Stat.- Geol. N. ¥., p. 249. 

 Paterina, Hall and Clarke, 1892, Eleventh Ann. Kept. State Geof. N. Y., p. 217. 



The description of the genus Iphidea and that of the type species 

 were combined. At the time of my study of Kntorgina and Iphidea I 

 did not agree with Mr. Billings in his reference of Oholm labradoricus 

 to Kutorgina,^ overlooking the fact that he had referred 0. lahradoricus 

 to Iphidea.'^ Since that time I have collected more material represent- 

 ing this group of shells, aud from its study have come to the conclusion 

 that Mr. Billings was correct in referring 0. lahradoricus to Iphidea. 

 The ventral valve of 0. labradoricus has a narrow false area of the same 

 type as Iphidea bella, and tlie characteristic pseudodeltidium is clearly 

 shown in a section, and it is known to occur in J. sculpt Hi s. Meek, I. 

 ornatella, Linnarsson, and I. pannula, White. The extreme develop- 

 ment of the false area and pseudodeltidium is found in an undescribed 



1 Bull. U. S. Geol. Surv., No. 30, 1886, p. 100. 

 "- Pal. Foss., II, Pt. 1, p. 76. 



Proceedings U. S. National Museum, Vol. XIX— No. 1 120. 



