[marræew] ORDOVICIAN SYSTEM ON THE ATLANTIC COAST 263 
there isan incipient calcification and thickening of the edges and a median 
ridge. 
Sculpture.—The surface ornamentation of longitudinal striæ is as de- 
scribed by Billings, but transverse growth lines also are present, and give 
the surface of the shell a cancellated appearance. 
Size—In the specimens sent from Newfoundland the length is as 
given by Mr. Billings, but the width is greater, Length of the ventral 
valve 27 mm., width 25 mm. The dorsal valve is about 3 mm. shorter. 
An example of the ventral valve in the museum at Ottawa has a length 
of 30 mm. and a width of 28. Depth approximately 3 mm.’ These 
dimensions exceed those of any Lingulella known to me, but are such as 
would be looked for in shells of the Trimerellidæ, 
Locality—The gray white weathering sandstones of Great Bell 
Island, Conception Bay, Newfoundland. 
The genus Trimerella to which this one is allied, is found in the 
Silurian (Upper) in Ontario, Sweden, ete. 
SPHÆROBOLUS, n. gen. (provisional.) 
This orbicular species is so different from the preceding (if Mr. 
Billings and the author have correctly interpreted the valves described as 
the ventral and dorsal valves respectively of this species) that it must be 
placed in a different genus. The unusual distinctness of the vascular 
trunks and their branches in the supposed ventral valve, the advaneed 
position of the central group of muscles in this valve, and the rarity of 
this valve in the material examined, also allow some doubt to remain as 
to whether this valve is a ventral. But it is evidently the valve which 
Mr. Billings regarded as the ventral of this species. Regarded in this 
light the genus finds its nearest relative in Dinobolus of Dr. Hall, which 
has valves of similar form; the resemblance to the Newfoundland 
species can be traced in the crescent and its scars and in the platform and 
its inequalities. 
The thickened umbo of this form, especiaily in the dorsal valve, 
appears to have had spaces between the layers (now filled by a powdery 
siliceous deposit) that compare with the cavities in the umbones of 
Trimerella and other brachiopods ; but we do not observe any vault or 
excavation beneath the thickened visceral part of the valves. The type 
of the genus is Lingulella (?) spissa, Bill. 
SPHÆROBOLUS SPISSUS, Pl. I., Figs. 5a—c. 
Lingulella ? spissa, Billings, Palæoz. Fossils, vol. ii., pt. i., p. 66, figs. 36a to c. 
Mr. Billings’s description of this species is as follows: 
“Shell subpentagonal or subovate, length and width about equal, 
sometimes strongly ventricose. Dorsal valve with the front margin 


1 Measurements by Dr. Ami of the Geological Survey. 
