ART. 4 CAMBRIAN CONCHOSTRACA — ULRICH AND BASSLER 23 



As based on specimen A, we find that Bradoria robusta is the same 

 species to which Matthew subsequently appHed the names Leperditia?? 

 rugosa, Bradorona perspicator mut. maxima, B. perspicator mut. major, 

 and B. perspicator mut. magna. It is the largest of all the known 

 St. Lawrence Atlantic province Bradoriidae. 



Careful comparison and further cleaning of the types of the three 

 supposed mutations of B. perspicator {maxima, major, and magna) 

 prove to our full satisfaction that they are three examples of a sin- 

 gle indivisible form or "mutation," and this a species that we think 

 is readUy enough distinguished from the types of B. perspicator. 

 This other species, for which the earliest name robusta is selected, 

 differs in being more oblique, more convex, and larger. Its normal 

 form is a composite of Figures 3 and 4 of Plate 1 on which the three 

 "mutations" are figured. The original of Figure 5 (mutation magna) 

 was injured on the cardinal edge. Restoring this and removing matrix 

 covering the post ventral edge, we have a nearly exact correspondence 

 with Figure 4. 



Another form figured on this plate, namely, Leperditiaff rugosa, 

 almost certainly belongs to the same species as B. robusta. The origi- 

 nal unfortunately is in bad condition, having evidently been crushed 

 and distorted by pressure. This, like several other specimens of these 

 peculiar Cambrian branchiopods, indicates by the crinkling of its shell 

 that the same was much more pliable than any ostracod shell known 

 to us; but there is so little doubt as to its original shape that we can 

 not hesitate in referring it to the same species as B. robusta. The 

 crushing of the type of L. rugosa, as is indicated by the accumula- 

 tion of wrinkles, was especially effective along the ventral border, the 

 consequent shortening of this thus giving the different outline as 

 figured by Matthew. The name robusta is selected for the reason 

 that in 1898 Matthew applied this name, under Aparchites, to another 

 example of the same species. 



A number of excellent specimens in the Walcott collection clearly 

 proves that the surface ornamentation of B. robusta is essentially of 

 the same concentrically rugulose pattern found in B. rugulosa. This, 

 however, is a larger species and differs further in the obtuse angulation 

 of the central part of the anterior edge, and the straightness of the 

 outline between this angle and the anterior extremity of the hinge. 

 Good specimens also exhibit a spine at the posterior extremity of the 

 hinge not observed in B. rugulosa. 



Occurrence. — Lower Cambrian (Hanfordian Clb): Kennebecasis 

 River {Aparchites robustus); Upper Etcheminian, Indian Brook 

 (i. rugosa); Lower Etcheminian, Dugald Brook {B. perspicator 

 magna and B. perspicator maxima)] Upper Etcheminian, Dugald 

 Brook, Nova Scotia (B. perspicator major). 



