R. G. Carruthers — A Revision of some Carboniferous Corals. 23 



Haime's publications, and as these latter still remain to many English 

 readers the chief work on Palseozoic corals, it must be said that, 

 although found in the larger paloeontological textbooks, Kunth's work 

 has not, perhaps, received in this country the attention it deserves. 

 According to this law, the insertion of new septa in a Rugose coral 

 takes place at three points in the circumference of the corallum, 

 approximately 80° apart, the chief of these being at the cardinal 

 septum, with the remaining two points on each side at the alar septa. 

 New septa are successively added on each side of the cardinal septum, 

 the youngest being always next to that septum. On one side only of 

 each of the two alar septa new septa are also added, the youngest 

 always next to those septa, on the side remote from the cardinal 

 septum. Since these young septa are necessarily short, there is 

 consequently, in transverse sections, a break in the grouping of the 

 septa at each of these three points. These breaks form the fossulm, 

 the largest being naturally at the cardinal septum ; this is called the 

 cardinal fossula, or more simply ' the fossula.' The other two breaks, 

 comparatively inconspicuous, are similarly referred to as the ' alar 

 fossulce.' Occasionally a fourth fossula is developed immediately 

 opposite the cardinal septum, and is called, from the primary septum 

 dividing it, the counter fossula. No new septa are ever developed 

 here, although the minor septa flanking the counter septum are 

 occasionally more elongated than the others. These fossulse are 

 further marked by depressions of the tabulae, varying in degree in 

 different specimens. 



The development of new septa according to Kunth's law may also 

 be seen on the exterior of any rugose coral with good longitudinal 

 ribbing, since each alternate groove corresponds to the position of 

 a major septum ; in any case, the arrangement can be seen on 

 removing the epitheca by acid or filing, so as to display the septa 

 within. 



Fig. 1. Fig. 2. 



Fig. 1, Diagram A. — Transverse section of Zaphrentis omaliusi. Primary septa: 

 H, cardinal septum ; G, counter septum ; A, A, alar septa ; L, L, counter- 

 lateral septa, a-c, the remaining major septa are lettered in the order of 

 their formation. The minor septa are indicated by the ridges at the bases 

 of the interseptal chambers. F, cardinal fossula ; A-F, A-F, alar fossulse ; 

 C-F, counter fossula. 



Fig. 2, Diagram B.— Tabula of Z. omaliusi, represented by contours (ifter 

 Vaughan). The deep depression is at the cardinal fossula, the three smaller 

 ones at the alar and counter fossulae. (See infra, p. 26.) 



