76 
ANNALS NEW YORK ACADEMY OF SCIENCES 
of the visceral chamber. A vertical section shows that the lateral processes of the 
septa are arched and ascendant; those situated toward the upper end of the coral- 
lum terminate at the edge of the septa; those situated lower down unite near the 
center of the visceral chamber, so as to constitute irregular tabulae. The inter- 
septal loculi are filled up with these lamellate processes, which are situated at about 
half a line apart, and united by closely set simple dissepiments that form right 
angles with them. Diameter of calice from 1 to 2 inches. 
While this description is exceptionally complete in so far as adult individ¬ 
uals are concerned, it, nevertheless, is of no value for the study of a genetic 
series. For such studies one must consider either a series of young individ¬ 
uals or the younger stages of adult individuals. The lateral processes or 
carinae of the septa are a very characteristic feature of the adults of this genus, 
but even a limited study of the earlier stages shows that at first these indi¬ 
viduals are without carinee, and if specimens of this age were collected they 
could not be distinguished from the Streptelasma forms occurring in the same 
horizon. The accompanying six figures drawn from transparent sections 
cut from typical individuals of this species illustrate six of the characteristic 
stages of the development. 
Figure 21a, sawed from the tip of one individual, shows the Streptelasma 
stage. In addition to the four primary septa there are present four pairs 
of secondary septa in the counter quadrants, two pairs of secondary septa in 
the cardinal quadrants and a pair of tertiary septa adjacent to the counter 
septum. No carinae are present, and the arrangement of the septa is in 
every way identical with that found in a corresponding stage of a Strepte- 
lasma. Figure 21b is a rather poor slide cut from a slightly later stage of 
another individual. The individual septa cannot be identified but the 
presence of tertiary septa in practically all of the spaces between the septa of 
the primary and secondary order is worth noting. 
Figure 21c, from a corresponding or possibly from an earlier stage of a 
third individual, shows the primary and secondary septa so that they can be 
easily recognized, while the tertiary septa are much longer than in the pre¬ 
ceding figure. No carinae are yet present, but in the section numerous fine 
lines cross between adjacent septa at intervals, and these may represent the 
origin of the carinae or the points at which they are about to develop. In 
figure 21d, the Streptelasma arrangement of the septa still persists. In 
addition to the four primary septa there are seven pairs of secondary septa 
in the counter quadrants and three pairs in the cardinal quadrants with 
tertiary septa in all the interseptal spaces. One ring or circle of carinae has 
appeared near the margin of the section. Figure 21e is a somewhat imper¬ 
fect section from a still later stage. The individual septa cannot here be 
positively identified, but in that portion of the section which has not been 
