ART. 4 CAMBRIAN CONCHOSTRACA — ULRICH AND BASSLER 95 



on most of the specimens, they are not mentioned in the description 

 because there is ground for the suspicion, if not the conviction, that 

 they are at least in part due to compression. 



Occurrence. — Middle Cambrian (Acadian): In the fine gray shales 

 of division Clc2 of Matthew's section at Hanford Brook, St. Martins, 

 New Brunswick. 



LEPIDITTA CURTA Matthew 



Plate 5, Figures 18, 19, Plate 7, Figure 29 



Lepiditta curia Matthew, Trans. Royal Soc. Canada, vol. 3, sec. 4, 1886, p. 62, 

 pi. 6, fig. 17; Trans New York Acad. Sci., vol. 15, 1896, p. 195, pi. 15, fig. 2. 



Description. — Valves obliquely semielliptical or subtriangular, with 

 the length and height, respectively, about as 10 is to 7 ; hinge straight, 

 the remainder of the outline rather gently curved except at the antero- 

 ventral angle, where it is sufficiently rapid to suggest the word tri- 

 angular in speaking of the outline. Surface now depressed convex, 

 originally probably rather strongly convex, marked with five or six 

 unequal concentric undulations. Umbo inconspicuous, situated about 

 one-fourth of the length of the hinge line behind the front angle. 



Dimensions: Length, 1.50 mm.; height, 1.02 mm. 



Remarks. — Onlj^ the two specimens marked by Matthew as the 

 types of the species have been seen. Matthew speaks of the interior 

 of the shell as having "roughened zones or undulations concentric to 

 the umbo." As the types retain very little of the shell and are merely 

 impressions of the exterior slightly roughened by remains of the 

 decomposed shell, the observation applies to the exterior rather than 

 to the interior. Respecting the affinities of the species, there can be 

 no reasonable doubt of its close reltations to L. alata. So far as shown 

 by the specimens, it differs from that species only in being a little 

 larger, relatively shorter and more triangular in shape and in having 

 fewer and coarser concentric undulations of the surface. Radial lines, 

 aside from those due to compression, are very obscurely indicated. 



Occurrence. — Middle Cambrian (Acadian): In the fine dark shales 

 of division Cld of Matthew's section at Porters Brook, St. Martins, 

 New Brunswick. 



LEPIDITTA? POUT A (Steusloflf) 



Plate 7, Figure 28 



Bythocypris polita Steusloff, Zeits. d. d. geol. Gesell., vol. 46, 1894, p. 775, 

 pi. 58, fig. 31. 



This species is known only from the description and figures published 

 by Steusloff. Judging from these the valves are obliquely semiellip- 

 tical, the anterior side descending rectangularly from the long, straight 

 hinge, the posterior side narrower and relatively acuminate at the 

 dorsal angle. Near the middle of the dorsal edge, two widely diverg- 



