cragin.] DESCRIPTIONS OF SPECIES. 63 
the known material represents the adult condition, or at least rather 
1m roe sizes of the shell, unless the two specimens described under the 
head of Trigonia rudicostata should be interpreted as the young of 
T. munita. This species with the two that follow belongs to the sec- 
tion Costatse. 
Trigonia rudicostata sp. n. 
PL XI, figs, l, 2. 
Shell small, ovate-pyramidal, nearly straight (slightly convex) on 
the postero-dorsal, broadly convex on the ventral, and less broadly so 
on the anterior side, inflation intermediate in degree; beaks situated 
at rear limit of the anterior fourth, prominent and acute at the com- 
pressed and transversely placed summit, excavated on the posterior 
side, turned inward and somewhat backward ; area nearly flat, shallow- 
concave on its proximal part, wide, making with the preareal sur- 
face an angle greater than a right angle, and separated from it by a 
compressed, prominent radial costa, which is larger than any other 
costa of the shell, the area posterior to this costa being ornamented 
with \ or 5. similar but narrower and smaller rays, between each two 
of which are 3 to 5 still smaller, strongly elevated, linear rays or 
costclkc, the intercostellar spaces being at least as wide as, or for the 
most part wider than, the rays themselves, preareal surface orna- 
mented with about 25 strongly elevated, round-topped ribs which 
[parallel the basal margin and are mostly slightly wider than the 
intervals between them. There are 7 of the horizontal or concentric 
[ribs in the lower half in one specimen and 10 on the lower 10 mm. in 
another. 
Measurements. — Height, 23 mm.; length, 27 mm.; breadth, 16.5 
lam. 
Occurrence. — The two specimens in the collections were obtained 1J 
pmiles east of Malone station. 
Although the material thus far available for study indicates be- 
tween T. rudicostata and T. munita differences of both radial and 
fconcentric ornamentation too marked to be ignored, it is quite possi- 
ble that new material from localities known or yet to be discovered 
|nay show that these differences are due to conditions of age or indi- 
vidual variation; for it is noteworthy that, except the types of T. 
wudicostata, no Costatre even approaching what we should predicate 
for the young of T. munita, have been found. 
Trigonia conferticostata sp. n. 
Pi. XI. fig. X 
Shell small, subtriangular, of the section Costatse, apparently 
piore elevated than T. rudicostata; posterior area costellate with 
