EXTOMOSTKACA. 4<5 



is a puzzling fossil, and has caused some mistakes. A Coro- 

 nula has been found in the middle division of the crag which 

 has afforded so many cetaceous bones. Eemains of peduncu- 

 lated Cirripedes occur in older deposits, but are mostly scarce 

 and fragmentary. A species of Pollicipes is found adhering to 

 drift-wood, perforated by bivalves, in the lias ; another occurs 

 in the Oxford clay, attached in groups to drift-wood, and the 

 shells of Ammonites, which probably floated in the sea after 

 death. The chalk affords many species of Pollicipes and Scal- 

 ■pellum, a species of the anomalous genus Verruca, and the 

 only extinct genus of Cirripedes — Loricula (fig. 10, 6). This 

 remarkable fossil is found attached to Ammonites, and exhi- 

 bits only one side in any of the examples hitherto found. In 

 this unsymmetrical development and the imbrication of its 

 valves it more resembles Verruca than any other Cirriped. 

 " During the deposition of the great cretaceous system, the 

 Lepadidaz arrived at their culminant point : there were then 

 three genera, and at least thirty-two species ;" whereas at the 

 present day the Philippine Archipelago, which is the richest 

 marine province, affords but five species. 



Class III— CEUSTACEA. 



Gliar.-^- Body articulated, with articulated limbs ; head with 

 antenna? ; branchial respiratory organs ; sexes distinct ; 

 metamorphosis in most, in none resulting in fixed indi- 

 viduals. 



Sub-Class 1.— EXTOMOSTEACA. 



Char. — Body with more or fewer segments than fourteen ; 

 integument chitinous, forming in some a bivalve shell, 

 eyes sessile. 



Small bivalve entomostracous Crustacea are found in all 

 strata, and attain their maximum size in the older rocks. 



