STOMATOPOEl. 
15 
Figuees. 
PI, I. Fig. 10. Part of a zoarium encrusting a Bourgueticrinus, 
X 9 dia. Upper Chalk : Gravesend. Wetherell Coll. 
PI. I. Fig. 11. Part of a zoarium encrusting and partly 
embedded in an echinid plate, X 1 0 dia. Middle Chalk : Chatham. 
Vine Coll. 
Affinities. 
The relations between S. gracilis and S. granulata among 
Cretaceous Bryozoa are analogous to those between 8. waltoni 
and 8. dichotoma in the Jurassic series. 8. gracilis has longer 
and thinner zocecia than 8. granulata \ hut the difference cannot 
be rigidly defined. In Milne Edwards’ types of 8. granulata and 
8. gracilis the ratio of zooecial length to diameter is 1 : 2/2^ 
and 1 : 3 respectively. In most of the specimens subsequently 
referred to 8. gracilis the ratio is higher, and 1:4 is a low 
average. Dimensions seem to me of far less value than is attached 
to them by some authors, e.g. MM. Pergens and Canu. This 
species illustrates the point. For, according to M. Pergens’ 
dimensions of the specimens he includes in the ‘ species,’ the 
ratio of length to diameter is four times as great as in Milne 
Edwards’ type. I should not feel inclined to retain the ‘ species,’ 
were not the differences in zooecial dimensions accompanied by 
other characters ; thus, in 8. gracilis the zoarium is more open 
and less crowded, and the zooecia are often subpyriform, although 
cylindrical in young and thin zoaria. 
8. gracilis differs from 8. calypso by having less elliptical 
zooecia, and from 8. divaricata by having longer zooecia. It is, 
however, more closely related to the Aulopora divaricata^ von 
Beuss,^ from the Hungarian Leithakalk, that has been renamed 
as 8. reussi,'^ which has more regularly cylindrical zooecia, and 
is better regarded as a Cainozoic elongate form of 8. granulata. 
Among Cainozoic Bryozoa 8. gracilis is probably most closely 
allied to the Bryozoan described by Manzoni^ as AEtea sica, 
' VonReuss. Foss. Polyp. "Wien. : Naturw. Abh. vol. ii. (1847), p. 53, pi. yii. 
fig. 18. 
Cat. Jur. Bry. p, 55. 
3 Manzoni: “I Briozoi del Pliocene antico di Castrocaro ” (Bologna, 1875), 
pp. 6, 41, pi. vii. fig. 69. 
