176 IV. I. Robinson, M^ 



Grouping of Septa in Early Stages. — None of these arguments 

 was decisive and nothing definite was known of the grouping of 

 the septa in the early stages of growth — the most important fact 

 of all — until the matter was taken up by Freeh (1890). A cross- 

 section was figured (Fig. 4) by him showing an arrangement of 

 the septa in quadrants. In the same paper a specimen of C. den- 

 ticulata was figured which shows, on the exterior, diverging lines 

 indicating conclusively a pinnate addition of the septa such as 

 appears in a similar way on the exterior of coralla of the genus 

 Streptelasma. 



Fig. 4. Calostylis denticulata. X 2. (After Freeh.) 



A Specimen of C. denticulata in the Yale collections shows this 

 especially well (PI. I, Fig. 5). It may also be seen, although not 

 distinctly, in two specimens (Cat. No. 42.569) in the United 

 States National Museum. Specimens of C. lindstromi from the 

 Girvan district in Ayrshire, Scotland, do not show definite striae 

 which can be traced far enough to prove such a structure. It has 

 not been seen among a number of specimens of C. spongiosa from 

 the type locality, but these are much more irregular in their 

 habit of growth than C. denticulata and the external markings 

 are obscured by a more complete epitheca. 



A specimen of C. denticulata from the type locality was rubbed 

 down at the tip with emery powder and as soon as structure 

 could be seen upon the surface when covered by a film of water, 

 it was polished and photographed (PI. I, Fig. 6). The original 

 from which the figure was made is mounted upon a slide and 

 is in the Yale collections. It shows undisputable bilateral sym- 

 metry and a very plain grouping into four quadrants correspond- 

 ing with the arrangements of Freeh's drawing (Fig. 4, above), 



