MUSEUM OF COMPARATIVE ZOOLOGY. 31 
of the cast, the outside margin of the coil thickens a little, forming an indis- 
tinct border along the margin of the shell, which becomes more evident as it 
approaches the orifice. The edge of the whorl is compressed and rather nar- 
rowly rounded. The surface of the shell is marked by fine, transverse, closely 
set strie, which apparently are directed backward towards the earlier formed 
parts of the shell, but in reality indicate various stages of growth of the shell, 
The interna! cast does not show these fine strie; but broader and more widely 
separated elevations, having the same direction as the striz. The diameter of 
the shell is 3.2 mm. ; the height isa little less than] mm. Owing to the shape 
of the shell it is difficult to measure its height accurately. 
Locality and position. — Station No. 1, North Attleborough, Mass., Cam- 
brian, one specimen. The discovery of another coiled gasteropod in this divis- 
ion of the Cambrian of America is of interest, and makes the sudden influx of 
coiled genera in the Upper Cambrian less inexplicable. 
11. Hyolithes quadricostatus, sp. n. 
Plate Il. Fig. 15. 
Shell straight, elongate, tapering gradually to an acute point; apical angle 
17°. The external cast of the type specimens is 20mm. long; including an 
additional length represented by an internal cast of the same specimen, but 
extending farther from the apical extremity, it is 25mm. long. As the end of 
cast is broken, a length of 30mm. may be presumed for the entire specimen. 
The supposed dorsal side is broad and flat or slightly concave along the centre; 
when depressed, a low elevation may occur along the median line; in all cases, 
the surface retains a rather flat appearance. The lateral angles are rounded. 
The supposed ventral side is as usual flattened along the median line for about 
half the width of the shell. The sides of this flattened surface are more or 
less elevated, giving it a slightly concave appearance along the median line. 
Immediately beyond the flattened surface on either side is a more or less dis- 
tinct groove. The result is, that, in addition to the two lateral angles, there are 
two angles or ridges on the ventral side, giving the entire shell the quadri- 
costate appearance indicated by the specific name. The two ventral ridges in- 
crease in distinctness as they recede from the apical extremity, and are usually 
more distinct, or at least less rounded, than the lateral angles. At a distance 
of six or seven millimetres from the apical extremity, the shell is crossed by 
an apparently imperforate septum. The cast of this septum from the upper 
side had the appearance of a flattened surface with a slightly elevated border 
around the margin. The surface of the shell is marked by fine transverse 
strie. The longitudinal ridges are less prominent on the interior cast of the 
shell than on the exterior. 
Taken by itself this species would appear to be very distinct from the usual 
forms of Hyolithes, but in reality it forms only the extreme of a series of 
intermediate species, which begins with specimens characterized by numerous 
