BROWN, RUGOSE CORALS 
89 
say that Proto streptelasma, the ancestral genus, is a rugose coral having a 
hollow conical or horn-shaped calyx, straight or slightly curved, without 
septa or having only a few rudimentary ridges near the upper margin indica¬ 
tive of septa. 
Several hollow, conical, tube-like fossils have been found in the upper 
Cambric deposits which have been referred to as gastropods or pteropods 
because of their general resemblance to certain modern representatives of 
these groups. It is possible that certain of these may really be the fossil 
remains of the primitive ancestral coral which has been assumed and named 
P rotostreptelasma. 
Having assumed what may legitimately be considered the ancestral 
form, it is now possible to trace out the phylogeny of the Streptelasma group 
of rugose corals, basing the interpretation of the various steps in the develop¬ 
ment on the ontogenetic development of representative individuals from the 
various genera and species. The assumed ancestral genus Protostreptelasma 
during the early Ordovicic gave rise to the earliest known representative of 
this group, Streptelasma profundum. In this species the primitive non- 
septate condition is crowded into the very youngest stage of the ontogenetic 
development, while in the later stages the well-developed tetramerally 
arranged septa are the most prominent character. Four primary septa first 
appear, and these are followed by secondary septa added in pairs in the 
counter and cardinal quadrants. In the adult only a few of the septa reach 
to the center. The others extend down the interior of the cup and are 
attached each by its inner margin to the secondary septum next preceding 
it in the order of appearance. In this way nearly all the secondary septa 
are united in a pinnate manner and leave a well-defined open space along 
either side of the cardinal septum and a space on the dorsal side of each 
alar septum. The tertiary septa appear in the interseptal spaces in the 
same order as the secondary septa. They remain short and free throughout 
their whole extent and never appear to be attached to the adjacent secondary 
septa. 
Passing now to Streptelasma corniculum and S. rusticum, the most abun¬ 
dant representatives of the Streptelasma group in the upper Ordovicic 
limestones, we find an advance in development beyond the S. profundum 
condition along one particular line. As an adult form, S. corniculum is much 
larger than the species just considered; it has more numerous septa; they 
are more nearly radially placed and the counter quadrants are accelerated 
over the cardinal quadrants. At the first glance it seems to have lost the 
four-fold structure so characteristic of the earlier species. But when the 
ontogeny or individual development is studied, it is seen that each individual 
first passes through a stage corresponding to the adult condition of S. pro- 
