190 INVERTEBRATE PALAEONTOLOGY 



sembling operculate Corals more than other Mollusca ; 

 their morphogenetic analogues are to be found in the 

 Richthofeniid Brachiopods of the Permian. Like them, 

 Radiolites and Hippurites were phylogerontic forms of 

 short duration. They were absolutely restricted to the 

 Cretaceous period, and played the part of rock-formers 

 in some districts. Though rare in the English Chalk, 

 they are not uncommon in littoral deposits such as the 

 Cambridge Greensand. Lucinacea were represented by 

 Tancredia (especially Jurassic), Lucina and Sphaera 

 (Lower Cretaceous). Among Cyclodonts the Cardiidae 

 (" Cockles ") were well developed, but they are rarely 

 common. Protocardia is locally abundant in the 

 Portlandian and Blackdown Greensand. Teleodonts 

 are rare in the Mesozoic, but representatives of most 

 families appeared in or before the Cretaceous period ; 

 while Corbula and many burrowing forms illustrated 

 the degenerate Asthenodonta. 



Scaphopods are rarely important fossils, but 

 Laevidentalium is locally abundant in the Lias, and 

 Antalis in the Gault. 



Mesozoic Gastropods are chiefly remarkable for the 

 decline of Aspidobranchs, and the rise of Ctenobranchs 

 and Tectibranchs. Pleurotomaria (PI. xiv. fig. 4) carried 

 on the Palaeozoic tradition, and maintained its import- 

 ance throughout the era; while Trochonematidae (e.g. 

 Amberleya and Cirrus] are abundant in the Jurassic, and 

 Trochidae, Neritopsidae and Neritidae occur locally. 

 Gymnoglossa are represented by Bourgetia in the 

 Corallian; Ptenoglossa by Scalaria (Epitonium) and 

 Solarium, both abundant in the Cretaceous. Many 

 important types of Taenioglossa appeared. Massive 

 species of Purpuroidea are common in the Great Oolite, 

 and Littorina, Capulus and Natica (PI. xiv. fig. 5) occur 

 in the Bajocian and Bathonian. The last series is 



