a number of the here mentioned species show plainly concentric lines of growth, 

 they on the other hand show a distinct radiate arrangement in Inversiula inversa 

 and Anarthropora monodon (PI. XXIII, figs. 10 a, 11a). These small plates which are 

 only distinct in quite young zooecia are each provided in the centre with a pore, 

 the edge of which has radiate rods, and to judge from Hincks' drawing the front 

 surface in the following species described by him is also divided into a number 

 of small plates each of which has a pore in its centre, namely, 'Lepralia% Palla- 

 siana (from Madeira), Sc/ifzo/jore/Za cindipora Hincks, -^Sch.^ concinna Hincks, Arthro- 

 poma circinnata Mac Gill., Lepralia subimmersa Hincks and »Le/).« gigas Hincks. 



In numerous species which appear in free colonies either the basal wall or 

 the frontal wall or both show a mode of calcification which we might call the 

 bilateral, as the wall in question is calcified in two lateral halves, which meet 

 in a longitudinal suture and as a rule each lateral half seems again composed 

 of a row of pieces the dividing sutures of which meet the longitudinal suture 

 obliquely. We may cite the structure of the basal wall in Fhistra foliacea (PI. 

 XIX, fig. 9 a) as an example of this form of calcification. On this wall we find 

 two systems of extremely fine stripes, which meet under proximally directed angles 

 and divide the wall into two lateral halves, separated by a longitudinal suture; 

 the two halves are again composed of a row of pieces, and these are separated 

 by distally directed, slanting svitures which end in the main suture. Each of 

 these lateral pieces is further joined to one of the pieces in which the respective 

 lateral walls are divided. We can be sure that the above-mentioned fine stripes 

 are lines of growth by treating the growing end of a branch with eau de Ja- 

 velle; for after this has dissolved the uncalcified parts, the basal wall of the 

 terminal zooecium shows an angular incision which corresponds with the angle 

 between the two systems of stripes. This form of calcification which can also 

 present a number of modifications is for ifistance found in Flustra Barleei, Fl. mem- 

 branaceo-trancata, FL papyracea, Discopora verrucosa, Dis. pavonella, Dis. scabra, 

 Smittina propinqiia (PI. XIX, fig. 3 a), Sm. reticulata, Sm. palmata (on the frontal 

 wall), Arthropoma Cecili, etc. and no doubt it appears in most cases on the frontal 

 wall in species furnished with marginal pores, each of which serves as the start- 

 ing-point for a suture which in most cases ends in the median suture. Still, a 

 median suture may be absent in very short zooecia and we find instead a number 

 of fan-shaped, converging suture lines, as in Discopora pavonella (PI. XIX, fig. 2 a). 

 With exception of the walls which are provided with specially small pores 

 (Thalamoporella, Steganoporella), all the surfaces (frontal walls, ooecia), which are 

 furnished with scattered pores, are also provided with numerous sutural lines, as 

 these start from each pore, and except for those which end in the free edge of 



