BILLINGSELLID^. 735 



Specimens that are somewhat doubtfuhy referred to Nisusia {Jamesella) nautes occur at 

 the following localities : 



(15c) Limestone in the Marjum limestone, near Swasey Spring; and (Ilq) about 2,350 feet (716.3 m.) above 

 the Lower Cambrian, and 2,050 feet (624.8 m.) below the Upper Cambrian in the limestone forming Ic of the Marjum 

 limestone [Walcott, 1908f, p. 180] ridge east of Wheeler Amphitheater; both in the House Kange [Walcott, 1908f, Pis. 

 XIII and XV], Millard County, Utah. 



(57f) About 2,200 feet (670.6 m.) above the Lower Cambrian, and 2,800 feet (853.4 m.) below the Upper Cambrian, 

 in the limestone forming 1 of the Stephen formation [Walcott, 1908f, p. 209], about 0.5 mile (0.8 km.) east of the 

 ' ' fossil bed, ' ' on the northwest slope of Mount Stephen, above Field, on the Canadian Pacific Railway, British Columbia, 

 Canada. 



y Nisusia (Jamesella) pellico (de Verneuil and Barrande). 



Plate XCVII, figures 2, 2a-b. 



Orthidna pellico de Verneuil and Barrande, 1860, Bull. Soc. gfol. France, 2d ser., vol. 17, pp. 535-536, PI. VIII, 

 figs. 7, 7a-b. (Described and discussed in French as a new species; see below for translation-. Figs. 7, 7a-b 

 are copied in this monograph, PI. XCVII, figs. 2, 2a-b, respectively.) 



The original description by de Verneuil and Barrande follows: 



Shell rather small, transverse, breadth greater than length by one-fourth, cut off squarely at the extremities. 

 Hinge crest attains the greatest breadth of the shell. Ventral valve twice as deep as dorsal valve, provided with an 

 area of twice the height, which rises perpendicularly and forms a right angle with the hinge crest. The opening is 

 only partly covered with a deltidium, which descends from the tip of the beak. On the other valve the bare rudi- 

 ments of a similar deltidium may be perceived. 



Neither valve has a sinus, and their commissure presents no wavy contours. 



The surface is ornamented with rather wide-spaced strise. Three or four principal striae are counted on the sides, 

 and two or three intermediate finer ones. The median region is bounded by two pronounced strise, between which 

 two or three fainter ones are distinguished. 



Dimensions: Breadth, 11 mm.; length, 8 mm.; thickness, 5 mm. 



Relations and differences: In having its area partly covered with a deltidium this species comes within the genus 

 OrtMsina, as understood by Mr. Davidson, but it no longer shows the needle-shaped hole of the tip, on which d'Orbigny 

 had established the genus. However, the analogy which it maintains with the preceding species does not admit of 

 its being placed in any other genus, and shows how slight is the importance of the characteristic used by the author 

 just named. The position of the area, with regard to the hinge, recalls 0. adscendens, which is clearly distinguished 

 from our species by the nature of its striae. 



From this last-named point of view 0. pellico approaches the LeptKnee more than it does most of the other Orthis 

 or Orthisina species. 



Observations. — As far as the illustrations and description can determine, this species belongs 

 with the nonspinose forms of Nisusia grouped under the subgenus Jamesella. 



The authors of the species state [1860, p. 536] that tliis shell was found in the red hmestone 

 with their "Orthis primordialis ." 



Formation and locality. — Middle Cambrian: (350 [de Verneuil and Barrande, 1860, p. 538]) Red limestone of 

 the Paradoxides zone, near Adrados, north of Sabero and Bofiar, Cantabrian Mountains, Province of Leon, northwestern 

 Spain. 



Nisusia (Jamesella) perpasta (Pompeckj). 



Plate CI, figures 1, la-h. 



Orthis perpasta Pompeckj, 1896, Jahrb. K.-k. geol. Reichsanstalt, Bd. 45, pp. 515-516, PI. XV, figs. 15-18. (Described 

 and discussed in German as a new species; see below for translation. Fig. 16d is copied in this monograph, 

 PL CI, fig. Ig.) 



Nisusia (Jamesella) perpasta Pompeckj, Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 254-255. (Original descrip- 

 tion, Pompeckj, 1896, pp. 515-516, copied, and species discussed as essentially on p. 736.) 



The original description by Pompeckj follows: 



Outline subrectangular, with straight hinge line and slightly bent frontal margin; cardinal angles slightly drawn 

 in; the length is little more than half the breadth, the greatest breadth being in the middle of the valves. Both valves 

 are very strongly arched. 



The ventral valve has a high, steep area, with a large triangular foramen, and the areal edges are rather sharp. 

 The apex is not drawn forward beyond the hinge line. . From the apex to the frontal edge there is a sinus which 

 gradually increases to a considerable breadth. The dorsal valve, which is also strongly arched, has a very low and 



