BILLlNGSELLIDiE. 733 



Msusia (Jamesella) kuthani Pompeckj, Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 253-254. (Original descrip- 

 tion, Pompeckj, 1896b, p. 514, copied, and species discussed as below.) 



The original description hj Pompeckj follows: 



Outline subrectangular, hinge edge straight with angles protracted but a short distance; length to breadth as 

 3 :4, often less. 



Ventral valve highly arched. Apex drawn forward, but not curved toward the dorsal valve at all, or in rare cases 

 but slightly. Area high, steep, with sharp areal edges and high, triangular foramen. Owing to the state of preserva- 

 tion, the details of the interior of the valves can not be well observed. 



Dorsal valve flatter, with rather decided arching on side edge and frontal edge, with sinus always distinct, which 

 corresponds to a faint swelling at the frontal edge of the ventral valve. The area is very low with a small triangular 

 foramen. Crural processes narrow, considerably divergent. 



The surface is ornamented with narrow sharp ribs, increasing by interpolation. The ribs are divided by inter- 

 spaces which are considerably broader than the ribs. In the interspaces there is frequently seen a lower, threadlike 

 rib. The number of ribs is 30 to 36. The ribs are mostly very distinct on the internal casts also. Sometimes internal 

 casts are found which show remarkably few ribs, and which in this respect and also in their greater breadth approach 

 Orthis perpasta var. macra. 



The present species has thus far been called, after Kusta's example, Orthis romingeri, but it differs from that 

 species (a) in the ventral valve, its apex never being so strongly curved as in Orthis romingeri, and in most cases not 

 curved at all; (b) in the dorsal valve, which in the present species is more strongly arched with a more decided sinus; 

 (c) in the sculpture, inasmuch as the ribs are narrower, sharper, fewer in number, and separated by wider interspaces 

 than in Orthis romingeri Barrande. 



Oiservations. — In the material of this species sent me by Doctor Pompeckj there is one 

 cast of a ventral valve that shows that a convex deltidium covered about two-thirds ot the 

 delthyrium; its front margin was arched so as to leave considerable space open between it 

 and the plane of the hinge line. 



There is a decided mesial sinus in most specimens of the dorsal valve, but in some it is 

 flattened so as scarcely to break the uniform low convexity of the valve; the strength of the 

 mesial elevation of the ventral valve also varies from a marked ridge to a flattened median 

 space. 



The species appears to be quite distinct from any described Cambrian form. 



The specific name was given in honor of Mr. Wilhelm Kuthan, of Tejfovik, Bohemia, 

 Austria- Hungary. 



Formation and locality. — lower Cambrian : Conglomeratic sandstones and graywacke inclusions in the lower 

 conglomerate zone of the Kamenna hurka at the following localities [Pompeckj, 1896b, p. 514]: (345i)o near Tejfovik, 

 and (345j) at Gross Lohovic, southwest of Skrej; both in Bohemia, Austria-Hungary. 



(345k)'' Sandstones at Slapnicky mlyn, near Skrej, Bohemia, Austria-Hungary. 



NisusiA (Jamesella) lowi Walcott. 

 Text figures 61A-D, page 734. 



Nisusia {Jamesella) toioi Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, p. 98, PL IX, fig. 14. (Characterized 

 and discussed essentially as below as a new species. Fig. 14 is copied in this monograph as fig. 61A.) 



The description of the form, outline, convexity, and cardinal area of the ventral valve 

 of Nisusia festinata (Billings) (PL C, figs. 1, la-e) is so applicable to this species that I will 

 refer the student to it for the description of those features. The surface of Nisusia {James- 

 ella) lowi differs from that of N. festinata in having more and finer radiating ribs, clearly defined, 

 rounded, concentric striiE and lines of growth, and in the absence of all traces of the surface spines 

 so characteristic of N. festinata. The latter is also a larger species. Nisusia (Jamesella) 

 lowi averages 10 to 12 mm. across the hinge line and rarely over 8 mm. in the length ot the 

 ventral valva of the large shells of the species. 



There is a close relationship between Nisusia alberta (Walcott) (PL C. figs. 3, 3a-d) and 

 N. (J.) lowi in form and size. N. alberta has a spinose surface, and the beds in which the two 

 species occur are separated by 1,700 feet of limestone. 



" Localities 345i and 345k are represented in the collections of the United States National Museum. 



