. Bulletin of the British Museum (Natural History), Geology. COLONIAL PHILLIPSASTRAEIDAE FROM DEVON 193 All the massive coralla described here are presumably surrounded by a holotheca (Hill 1935 : 497) although it has only been observed in Frechastraea micrommata (C. F. Roemer) and in two sections of F. goldfussi. It is fibronormal in character and somewhat variable in thickness in the range o*i-o*i5 mm. Both the septa and the pseudotheca abut with a shallow convex surface against the holotheca, or penetrate slightly to form a wedge-shaped depression in its surface. Thamnophyllum germanic
. Bulletin of the British Museum (Natural History), Geology. COLONIAL PHILLIPSASTRAEIDAE FROM DEVON 193 All the massive coralla described here are presumably surrounded by a holotheca (Hill 1935 : 497) although it has only been observed in Frechastraea micrommata (C. F. Roemer) and in two sections of F. goldfussi. It is fibronormal in character and somewhat variable in thickness in the range o*i-o*i5 mm. Both the septa and the pseudotheca abut with a shallow convex surface against the holotheca, or penetrate slightly to form a wedge-shaped depression in its surface. Thamnophyllum germanicum schouppei, T. caespitosum, T. caespitosum paucita- bulatum and Peneckiella salternensis have cylindrical corallites with fibronormal epithecae. The peripheral septal ends meet the epitheca and depress it slightly (Kato 1963, text-fig. 17/) in the same manner as the relationship between septa and holotheca in F. goldfussi. In all cases where the microstructure can be distinguished, the tissue of dissepi- ments and tabulae is fibronormal. (b) Increase. For full details of corallum increase it is necessary to cut serial sections but in the present material, this has been possible only with Thamnophyllum germanicum schouppei. Even in this subspecies, fracturing has so affected the point of branching that the details of septal insertion are obscured. Increase in the other taxa described here is known only from random sections cut through developing or immature individuals. Both axial and lateral increase are recorded and in some cases both may occur within the same colony. At the present time no detailed work has been done on increase in plocoid rugose corals. Most of the methods of increase observed in the present material, however, have been briefly described by Rozkowska (1953). The most common process is the development of one or more new individuals in the border area of two or more surrounding adult corallites (Text-figs. 5a, b). Rozkowska (1953 : 39, 71) called. Fig. 5. In
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