112 C. E. Gordon — Early Stagey in Paleozoic Corals. 



In figure 1 we have a 



" transverse section, through the tip of the corallum. The dark 

 median lines of only six primary septa are present, but the out- 

 lines of the septa as a whole are not clearly determinable, their 

 surfaces being fused throughout. The two median septa are 

 represented by a continuous line, while the other four septa are 

 arranged as an upper bilateral pair and a lower bilateral pair. Of 

 the six primary interseptal spaces the two upper are slightly 

 smaller than the others. By interseptal spaces may be here 

 understood the interval between the dark lines of two contiguous 

 septa ; the septa are so broad as to occupy the whole of the cali- 

 cinal cavity, leaving no interseptal loculi." 



1 The author explains that the terms 



"upper" and "lower" are used merely 

 for convenience and have no morpholog- 

 ical significance. I wish here to call 

 attention to Duerden's observation that 

 the two upper " primary " (of Duerden's 

 figures) interseptal spaces are smaller than 

 the others, as this fact lends some support 

 to a different interpretation of the figures 

 from that which Duerden had given and 

 which I ]3resently wish to discuss. 



" In all the figures the upper border cor- 

 responds with the convex side of the coral, 

 and the lower with the concave border ; the 

 primary septa are indicated by the Roman 

 numeral I, and the later septa by the letters 

 A-D, according to their order of appearance 

 within the four primary interspaces." 



The reader's attention is again called to the exact language 

 of the author, as great stress is laid by him upon the develop- 

 ment of these septa in four primary interseptal spaces, which 

 according to him do not represent the whole number, but only 

 four out of six such spaces. I think another interpretation may 

 be given to this early arrangement as exhibited in the apical 

 section studied by Duerden. 



In figure 2, which is a transverse section through the tip 

 of another corallum taken comparatively a little higher than 

 in the case of figure 1, two new septa are making their appear- 

 ance, apparently as a unilateral pair. This is probably to be 

 explained as a case of slightly unequal growth, as Duerden 

 remarks. The dark tadpole-shaped spaces represent the inter- 

 septal loculi and partly indicate the boundaries of the septa. 

 The dotted line in all the figures marks the outline of the 

 actual section. 



r 



Figure 1. Lopho- 

 p h y 1 1 u m p ro liferum . 

 T r an s v e r s e section 

 through the tip of the 

 corallum. After Duer- 

 den. 



