PLACENTICERATID. 215 
The lateral angles of the single costs, and still more the junctions of the 
dichotomous costs, when these occur, tend to rise up more prominently 
than the rest of the costation as in other forms, but they do not in the 
specimens examined, as in syrtale and intercalare, become tuberculose. The 
specimens from which these descriptions were taken are in the Museum of 
Comparative Zoology. 
This species is distinguished from P. placenta by the shorter and stouter 
lobes and saddles and the better separation of the sutures at all stages 
except, perhaps, the youngest. It stands apparently nearer to P. syrtale 
in its sutures than to intercalare, but this is due to the fact that in intercalare 
the sutures vary from those like syrtale to as complicated as: in Meek’s 
figures, and if the comparisons are made with the former, it is seen that the 
external characters and sutures place it between intercalare and whitfieldi, on 
account of the suppression in both of the lateral line of tubercles. A speci- 
men from Dallas County, Tex., has similar markings and sutures so far as 
seen on the young volutions, and is probably the gerontic stage of this 
species. It is an incomplete living chamber about one-half of a volution in 
length, with the inner volutions attached but badly crushed. The latter 
_shows the large inner row of nodes and the sutures in part, and these last 
agree closely with those of the specimen described above. 
The volution trom line of involution to venter at base of living chamber 
is 75 mm. in diameter, transverse diameter about 40 mm., and at one-fourth 
of a volution distant from this the diameter is 91mm. The venter is broad, 
and the ventral zone convex on the cast at the two last septa. The 
tubereles are almost obsolete and the costze completely gone, the cast 
being smooth with the exception of one obscure broad longitudinal ridge 
on the centran surface of the lateral zone. The remnants of tubercles 
are shown in obscure and very slight folds with a decided apical trend. 
This description shows that the gerontic stage is quite distinct from that of 
placenta or whitfieldi. 
The basal suture is very complex in its outlines, but has the short 
saddles and lobes of this species. The next younger septum is, however, 
closely approximated to the last. The first and second lateral lobes are 
very narrow and the saddles approximate. The lateral lobe is also narrow. 
The remaining lobes and saddles are more like those of the younger stages, 
but also have narrower lobes and broader saddles. These sutures are quite 
