STOMATOPORA. 47 



zoarium with ocecium, x 25 dia. Bradford Clay : Box, Wilts. 

 Holl Coll. B. 4860. 



Affinities. This species is the type of the genus. It belongs to 

 a group of species which has lasted from the Jurassic to the 

 present day. It is represented in the Cretaceous by a group 

 of forms described by D'Orbigny as different species, but now 

 included as Stomatopora granulata, M. Edw. 1 In the Cainozoic 

 representatives of the genus are much scarcer than in the Cre- 

 taceous ; nevertheless the group of species to which S. dichotoma 

 belongs is represented by Stomatopora divaricata (Reuss), 2 from 

 the Hungarian Miocene (Leithakalk), and by a living species, 

 identified by Johnston as S. granulata, M. Edw. In this 

 course Johnston has been followed by Hincks, Busk, and others. 

 The recent species, however, has the distal end of the zocecia 

 raised to a greater extent than the Cretaceous species, and the 

 zocecia are also more pyriform ; in Milne Edwards' specimen 

 the zocecia are regularly cylindrical. M. Pergens 3 has previously 

 expressed doubt as to the occurrence of the Cretaceous species 

 in recent seas. If the common English species is to be separated 

 from that described by Milne Edwards, then a new name will have 

 to be given it, as there is no available synonym. 



S. dichotoma differs from S. granulata (M. Edw. non auct.) in 

 having the zooecia more regularly cylindrical, and having the peri- 

 stomes, as a rule, less raised. It approaches more closely to the 

 variety figured by D'Orbigny as S. incrassata, to which it is nearly 

 allied. This is not the S. incrassata of Smitt, which is a 

 Proboscina. It differs from S. divaricata (Reuss) by the fact that 

 the Miocene species has a looser zoarium and longer zooecia. 



If the common recent English species is to be included with 

 the Cretaceous S. granulata, then both of these must also be 

 included with the Jurassic S. dichotoma. As, however, there are 

 definite differences between them, it appears better to keep them 

 distinct. 



1 H. Milne Edwards. Mem. sur Crisies : Ann. Sci. nat. Zool. ser. 2, t. ix. 

 1838, p. 205, pi. xvi. figs. 3, 3. 



2 A. E. Reuss. Foss. Polyp. Wien. Tert. : Haid. Naturwiss. Abh. Bd. ii. 

 1847, p. 53, pi. vii. fig. 18. . 



3 E. Pergens. Eevision Bry. Cret. D'Orb. : Bull. Soc. beige GeoL t. iii. 

 1889, Mem. p. 330. 



