360 ^Ii*- TJ- Gr. Canutliers on the 



treated by previous observers, among whom Duerden should 

 be specially iiieutioned. 



Tiie movements above referred to are in part shown by the 

 varying angles of inclination of tlie septa to the axial line. 

 These serve to express the fact that the first six or proto- 

 septa are developed differently from the later or " metasepta/' 

 The change is marked by the only developmental pause 

 observed. In other words, the primary septal plan of 

 these Rugose corals is hexamerous and is arrived 

 at by an insertion of bilateral pairs analogous to that 

 occurring in the soft parts of the rest of the Madreporaria 

 and, indeed, in most Anthozoa. 



There is commonly some irregularity in the growth of the 

 two lateral protoseptal pairs, and in some cases an indication 

 of a spiral, or, at any rate, an alternating arrangement. The 

 direction of the spiral, however, was found to vary in diffe- 

 rent specimens of the same sj)ecies, and may quite well be 

 an irregularity of no special significance, sucli as commonly 

 occurs in living corals. The important point is tiiat this 

 irregularity, when it occurs, is never so strongly marked as 

 to interfere with the sequence above given — i. e., the axial 

 septum appears first, followed by the alar primary pair, and 

 this by the counter lateral pair. Furtlier consideration of 

 this point may therefore be lett to future investigation. 



The septal sequence given above was originally observed 

 in some varieties of Zaphrentis P/iillipsi, Ed. & H., and has 

 since been found in several other species enumerated below, 

 toffether with the various stages found in each : — 



ri, Zap/i. rhillipsi, Ed. & II., and variants. Stages I. to III. 



I 2. Zuph. S]).i Stage III. 



■v, , ... J 3. Lophoplnillum eruca.'M'Qoy. Stages I. to III. 



Carbonilerous • ^ cJat/Loma sp.^ ^ ," I. to III. 



I 5. Uilni7iojJii/llu}n sp. Stage III. 



1.6. Ci/c/uji]ii///Hmfiin(/ites, Fleni. „ III. 



o-i . j 7. (':') Cij(it/iop/iyllum, sp.^ (a Weulock form). Stages II. & III. 



toilurian ^ g_ streptehtsma sp. (a IJandovery form). Stage III. 



Ordovician . . 9. StrepLelasma t?p. (a Llaudeilo form). Stages I. to III. 



^ A small, long and narrow, tuberculated form, wliioli I have been 

 unable to speciiicidly identifv. It is labelled " J'l/iyia " in the Jermvn 

 Street collection — an obvious mistake. Ileg. no. Idlbti Mas. Tract. LtcoI. 

 London. 



'^ This is the form referred to C. cor/iua, de Kon., by James Thomson, 

 and ligui'ed and described bv him as such in I'roc. Phil. Soc. Glasgow, 

 vol. xiv. (1882-83) p. 428 and tig. 29, pi. x. 



^ Provisionally referred to this genus. It is certainly specifically 

 distinct from the two species of" i>trept(J(is7na^' examined from ^Ii's. Gray's 

 collection. Reg. no. 16179 Mns. Pract. Geol. London. 



