712 CAMBRIA X BRA CHIOVODA— WA LCO TT. 



may be observed. The concentric stiite pass around over the false 

 area and cross the pseudodeltidium. Shell substance corneous. 



This specimen was received from Professor J. F. AVhiteaves as one of 

 the types of /. belhi. It differs, however, so materially from the descrip- 

 tion of that species and the figure illustrating- it that I found it neces- 

 sarj- to give it a distinct specific designation, and I take pleasure in 

 naming it after Sir William K. Logan. 



The specimen bears the label "Trois Pistoles, 18GS, T. C. Weston.'' 

 It was collected from a bowlder in tlie conglomerat*' at that locality. 

 It is probably of ^Middle Cambrian age, but this can not be stated with 

 certainty, as there are no associated fossils. Mr, Bdlings speaks of the 

 occurrence of fragments of trilobites in the bowlder containing this type 

 of/. Ix'Ua. He does not mention the j^enera or species. 



The species a|)proaches most nearly /. crrnistyin in its short pseudo 

 deltidium and finely striated surface. It differs, however, in the char- 

 acter of the surface stria', the form of the false area, and the pseudo- 

 deltidium. 



Formation and locality. — Conglomerates at Trois Pistoles on the St. 

 Lawrence, Province of Quebec. The conglomerates of this formation, 

 according to Sir William E. Logan, form nine separate layers, from - 

 to 1() feet thick, l)edded in gray, calcareous sandstone. The geclogic 

 age of the deposit containing the matrix is supposed to be ITpper Cam- 

 brian or Lower Ordovician. The age of the bowlders can be determined 

 only by the fossils found in each. 



IPHIDEA PEALEI, new species. 

 (Plate LIX, figs. 8, 3a-3c.) 



Ventral (pedicle) valve subconical, beak slightly incurving over the 

 pseudodeltidium. Cardinal slope fiattened to form a narrow false area, 

 which is clearly defined from the curvature of the shell by slightly 

 elevated thread-like ridges. Pseudodeltidium comparatively narrow, 

 strongly convex, and arched below. The stri.i^ of growth cross the 

 false area and arch over the delthyrium. 



Dorsal (brachial) valve moderately convex, and without any special 

 characteristics to distinguish it from the same valve in /. bella, I. 

 f^-'q)erh<(, and J. lahradorica. 



Surface marked by fine concentric striae and lines of growth that are 

 usually plain, but iu some examples are slightly crenulated. In such 

 instances fine radiating lines or stria' are also shown. Shell substance 

 corneous. 



In tlie most perfectly preserved specimens there is a slight slit or 

 depression near the apex of the ventral valve, but there is no trace of 

 a perforation or apical oi>eiiing. 



This species apju-oaches 7. ficidptilis iu some examples of the ventral 

 valve. It ditters mainly in the narrow pseudodeltidium and the char 

 acter of the surface markings. It miglit be considered as a fi)nii int^r- 

 me<liate between /. hella and /. .srHlptiHa. 



