44 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 78 



This is one of the more abundant species of this genus, and in its 

 typical form is readily distinguished from B. papilio by the rounding 

 of its ventral margin, its more erect— that is, less oblique — habit, and 

 less angular posterior ridge. The short anterior and posterior dorsal 

 ridges are well developed, and as compared with B.planata the poster- 

 ior one is much better defined than usual in that variety or closely 

 allied species. The five specimens in the Matthew collection marked 

 types are all of the same form. Matthew's main figure of the species 

 is accurate so far as outline is concerned, but is imperfect in repre- 

 senting the posterior ridge too narrow. The small obUque lines in 

 the dorsal depression also are somewhat misleading. 



Occurrence. — Lower Cambrian (Hanfordian, division C162-C164): 

 Hanford Brook, New Brunswick. 



Plesiotype.— Cat. No. 50549, U.S.N.M. 



BEYRICHONA TINEA TRIANGULA (Matthew) 



Plate 6, Figures 8-10; Plate 7, Figures 8, 9 



Beyrichona triangula Matthew (part), Trans. New York Acad. Sci., vol. 14, 

 1895, p. 135, pi. 7, fig. 5 (see also B. papilio). 



The three types of this form indicate two species. The specimen 

 marked "A" represents a rather common variety of B. tinea in which 

 the ventral portion is somewhat produced and hence more sharply 

 rounded. The anterior edge also is blunter. Typical examples of 

 this variety are readily distinguished, but in the Walcott collection 

 there are so many intermediate specimens that we do not feel justified 

 in according a higher rank to the form than that of a variety or muta- 

 tion of B. tinea. 



The other two specimens, marked "B" and "C," are unquestion- 

 able examples of B. papilio. The figure given by Matthew of B. 

 triangula is manifestly a composite of the characters of two distinct 

 species. Specimen A supplied the dorsal half, B and C the ventral 

 part. In A the ventral extremity was obscured by adhering rock. 

 When this was removed, the belief that this specimen, if not identical 

 with B. tinea, was at least more closely allied to that species than to 

 B. papilio, became strengthened to conviction, for it proved in every 

 respect identical with a form that we had distinguished as a variety 

 of B. tinea, and for which we propose to adopt Matthew's name. 



Occurrence. — Lower Cambrian (Hanfordian-div. Cl63): Hanford 

 Brook, New Brunswick. 



Plesioty pes. —Cat. No. 50550, U.S.N.M. {loc. 2'). 



