626 



WM. H. EASTON 



septa in very late mature stages. This species 

 appears to be related to Amplexus rock- 

 fordensis Miller and Gurley. The other three 

 species are apparently closely related mem- 

 bers of the Hapsiphyllidae. The nature of 

 septal insertion and the presence of cardinal 



CT IX 



CTCC 



Fig. la, b. — Principal systems of insertion of 

 septa in the rugose corals, la, "zaphrentid" 

 type; lb, "cyathaxonid" type; A, alar septum; 

 C, cardinal septem; CL, counter-lateral sep- 

 tum; CT, counter septum; 1-4, major meta- 

 septa; 1X-4X, minor metasepta. (Modified 

 from Hill, 1935.) 



fossulae and of alar pseudofossulae at some 

 stage in each of these species are strong argu- 

 ments for assigning such a relationship. 



Early septal insertion in these amplexoid 

 corals as found by the writer starts with an 

 aseptate condition, after which the axial 

 septum appears. The left alar is next in- 



serted, followed by the right alar, the left 

 counter-lateral, and the right counter- 

 lateral septa in that order. The first meta- 

 septum is inserted in the left counter 

 quadrant and the second metaseptum is in- 

 serted in the right counter quadrant. Axial 

 fusion of the primary septa tends to persist 

 into mature stages. This order of insertion is 

 somewhat at variance with that commonly 

 understood to obtain in that most writers 

 have found the alar septa to be inserted 

 simultaneously as a pair, followed by the 

 counter-lateral septa also as a pair. The 

 writer (Easton 1945, p. 385) found that the 

 right alar system was the first to be inserted 

 after the axial septum in Kinkaidia trigo- 

 nalis. 



Contratingent minor septa, which lean 

 toward the counter quadrants and are joined 

 to the next adjacent major septa are well 

 known and aid in rapid orientation of sec- 

 tions, but the writer is not aware that any- 

 one has pointed out the apparent contra- 

 tingent nature of tabular intersections near 

 the epitheca in those corals in which the pe- 

 ripheral edge of a tabula slopes from the 

 counter position proximally toward the 

 cardinal position. This feature can be used 

 to orientate sections (pi. 87, figs. 12, 13) in 

 which the septa are not capable of dif- 

 ferentiation on other grounds. 



The writer noticed several abnormalities 

 of septal relationships during this work. 

 The amplexoid trend is apparently increas- 

 ingly strong as maturity progresses, but 

 some septa in early stages may be with- 

 drawn after insertion. The position of a 

 septum may be clearly established from 

 study of septal grooves, but the actual in- 

 sertion of the septum may be retarded. Oc- 

 casionally, one will find in the counter 

 quadrants a metaseptum attached to the 

 alar septum for a time, rather than to the 

 next preceding metaseptum. The rate of 

 septal insertion is subject to wide extremes 

 of variation in a single species, as exemplified 

 by very rapid insertion of septa, followed by 

 very slow insertion. Examples in which one 

 of a pair of quadrants contains more meta- 

 septa than the other are common and are 

 usually indicative of contortion or genicula- 

 tion of the corallite. In the attached apical 

 portion of one species, the alar septa, 

 though presumably tending to be inserted 



