94 
Dimensions. —Length, 3‘33 mm. ; width, 3'33 mm. ; apical height, 1 mm. 
Relationships. — ■Acrothele woodworthi, Walcott, 1 a Lower Cambrian fossil 
from Massachusetts, is not far removed from the above species, but is not so 
distinctly quadrate nor so clearly defined as to its false area. The Middle 
Cambrian species, A. matthewi var. eryx, Walcott, 2 is remarkably near, but 
the apex is closer to the posterior margin. It is also a much larger form. 
Acrothele brews, sp. nov. Plate VI., figs. 5, 5a. 
Description. —-Ventral valve semicircular; width greater than length. 
Posterior margin nearly straight, anterior well rounded. Apex situated close 
to the posterior margin, hence the false area is broad and short. Anterior 
slope of shell distinctly convex, the posterior slope concave. Shell surface 
marked with concentric lines of growth. 
Dimensions. —Length, 2'16 mm. ; width, 3'16 mm. ; height at apex, 
'916 mm. 
Relationships. —-In the widely expanded shell, narrow false area and 
sub-central position of the apex of the ventral valve the above species bears 
some resemblance to Acrothele levisensis , Walcott, 3 from the Lower Ordovician 
shales of Point Levis, Quebec, Canada. 
* _ 
Fam. BlLLINGSELLIDiE. 
Genus Billingsella, Hall and Clarke. 
Billingsella tenera, Chapman sp. Plate VI., fig. 6. 
Orthis tenera , Chapman, 1904, Pec. Geol. Surv. Viet., vol. I., pt. 3, p. 223, 
pi. XXL, figs. 8, 8u. 
Observations.— The original drawings given in 1904 do not adequately 
express the median folding of this shell, and I have therefore redrawn it. 
The median fold is marked with a faint sulcus. In some respects the shell 
resembles Nisusia, but the internal structure shown is not sufficient to make a 
close comparison possible. The pedicle foramen is distinctly seen, as well 
as the depressions in the cast which mark the bases of the crurge, whilst a 
cardinal process seems to be shown in the specimen. 
Relationships. —In some respects the above species resembles B. tonhiniana , 
Mansuy 4 , but the plication of the Heathcote species is not so pronounced. 
The dimensions are about the same in both forms. Mansuy regards his 
species as Middle Cambrian. 
Billingsella fergtjsoni, sp. nov. Plate VI., figs. 7-9. 
Rhynchonella (ICamarotcechia) sp., Chapman, 1904, Pec. Geol. Surv. 
Viet., vol. I., pt. 3, p. 224, pi. XXI., fig. 10. 
Description. —Shell broadly ovate, cardinal line rather short, with cardinal 
extremities sloping to meet the widely rounded anterior margin. The 
postero-lateral areas bevelled, the median area depressed giving rise to two 
elevated areas diverging from the cardinal line to the extemities of the 
anterior margin. Shell-surface folded into eight prominent well-rounded 
riblets. The type specimen (7838) probably represents a dorsal valve, the 
paratype (refigured from Pec. Geol. Surv. Viet. 1904) a ventral valve. The 
latter has been further cleared of matrix since it was firs! figured, and this 
has confirmed its identity with the second (tiqoe) specimen. There is also a 
cast of an orthid (Xo. 7799) which may reasonably be assumed to belong 
to the above species. 
1 Cambrian Brachiopoda. Smithsonian Misc. Colls., vol. LIII., No. 1810, 1908, p S8, pi IX., fig. 11. 
2 Cambrian Fannas of China. Proc. U.S. Nat. Mus., vol. XXIX., 1906, p. 11. 
3 Camb. Brach. Sm. Misc. Colls., vol. LIII., No. 1810, 1908, p. 85, pi. VIII., fig. 13. 
1 Mem. Serv. Geol. de l’Indochine, vol. IV., fasc. II., 1915, p. 7, pi. I., f. 2 a-q. 
