CRANIA. 3G5 



closely resembling those of ivory in size and arrangement, 

 and passing obliquely through the laminae. Near the 

 margin of the shell these tubuli may be seen lying nearly 

 parallel to the surface.* 



CRANIA, Retz. 



Shell inequivalve, equilateral, orbicular ; the upper valve 

 patelliform, with an eccentric summit ; wrinkled, smooth, or 

 with radiating ribs or stripe (not sculptured in our native 

 species) ; under-valve flat, imperforate, adherent by its 

 entire external surface, fixed to various substances. No 

 hinge or ligament. Four muscular impressions in each 

 valve. 



Animal with two large horizontal cirrhated buccal 

 appendages, each forming a short spiral arm, curved 

 inwards, free and unprovided with any skeleton. 



This view of their relations is, however, on the point 

 of being combated by the celebrated Danish naturalist, 

 Professor Steenstrup, whose researches have, we believe, 

 led him to the unexpected conclusion that the Hippurites 

 and their allies are really related to tubicolons Annelida. 



This very curious genus is better known in the fossil 

 than in the recent state, though it is probable that all the 

 fossil Crania are improperly associated in the same generic 

 group. Those which have produced, and have free under- 

 valves, should form a separate section, and in them we see 

 a passage towards Calceola on the one hand, and the 

 Eudista on the other, which would go far towards esta- 

 blishing the brachiopodous nature of those curious fossils. 



* Carpenter, Brit. Assoc. Rep. 1844. 



