NO.1120. rROCEEDIXGS OF THE NATIONAL MUSEVM. 711 



that divide the surface into minute pits that give the impression of 

 iiuely woven cloth. T. ornateUa and I. pannula represent this type. 

 Among other genera it may be found in Treniatis; and the second type 

 of surface, as shown by I. sculptiUs, is frequently seen on Llngulella. 



IPHIDEA SUPERBA, new species. 

 (Plate LIX, tiys. 1, \a-e.) 



IpMdea cf. ? ornateUa, 1892, Hall and Clarke, Pal. N. Y.. VIII, Pt. 1, jil. iv, 

 figs. 6, 7. 



Ventral (pedicle) valve subcorneal, with a minute beak incurving over 

 the pseudodeltidium. Cardiiuil slope slightly flattened, so as to merely 

 indicate an imperfectly deiined, rather narrow area. In some specimens 

 the curvature of the shell is practically continuous to the base of the 

 pseudodeltidium. Pseudodeltidium broad, convex, with its lower mar- 

 gin broadly arched, so as to leave a considerable space between it and 

 the line of the general plane of the shell. 



Dorsal (brachial) valve slightly convex; most elevated a little in front 

 of the small beak which projects slightly over the broad open (?) del- 

 thyrium. No traces of a false area or a pseudodeltidium have been 

 observed. 



Surface with rather strong concentric striie, and a few somewhat 

 obscure lines of growth. On the ventral valve the striic extend around 

 to and cross the pseudodeltidium. Shell substance corneous. 



This is one of the larger species of the genus, being surpassed in size 

 only by I. labradorica. It is clearly distinguishable from I. bella by 

 its larger size, more depressed ventral valve, and the form of the 

 pseudodeltidium. The dorsal valves of the two species are quite simi- 

 lar. It differs from I. pealei in its broad pseudodeltidium, false area, 

 and surface markings. 



One specimen has a length of mm. and a little greater width. The 

 area is vertical, tbe pseudodeltidium being broken away. 



Formation and locality. — Middle Cambrian, Tonto Terrane, Ohuar and 

 and Nunkoweap valleys, Grand Canyon of the Colorado. (No. 20429, 

 U.S>N.M,) 



IPHIDEA LOGANI, new species. 

 (Plate LIX, figs. 2, '2a, 2l>.) 



Ventral (pedicle) valve conical, transverse in outline at base, almost 

 semicircular. Beak minute, incurving over the pseudodeltidium. 

 Cardinal slo])es rounded and flattened so as to form a fairly well 

 defined false area that is broken by a very wide triangular space. 

 Pseudodeltidium arched upward, forming a narrow, sloping shelf 

 beneath the beak, the angle of slope from the summit of the shell 

 over the beak and i)seudodeltidium being nearly the same as that of 

 the slope from the summit to the front. 



Surface marked by very fine concentric striie and somewhat coarser 

 lines of growth. Under a high ]>()wer slight traces of radiating striai 



