Mr. L. Reeve on the recent Cranise. 137 



Prof. Suess has observed that C. anomala ranges over this area 

 closely, both in locality and depth of habitat, with Terehratulina 

 caput-serpe7itis. \yherever one species is found between Spitz- 

 bergen and Vigo, the other is found also ; but C. anomala does not 

 pass with T, caput-seiyentis into the Mediterranean, nor to North 

 America; and he deduces some interesting conclusions from 

 this, in connexion with their fossil distribution, with the view of 

 showing the relations of their existence in time as well as in space. 

 Another species, which I refer to Polios Anomia turbinata, appears 

 in the Mediterranean, and it was dredged in the jEgean by Prof. 

 Forbes from depths varying between 50 and 150 fathoms. A 

 third species, C. 7'ostrata, is recorded from West Africa ; and a 

 species, which I have the pleasure of naming C. Suessiij has been 

 collected by Mr. Strange at Sydney, East Australia. No Crania 

 has as yet been found in the New World. C. radiosa, described 

 by Dr. Gould from Rio Janeiro, proves to be an Orbicula, which 

 genus is not uncommon in the waters of South and Central 

 America. 



In Terehratula and Rhynchonellaj it may be as well here to 

 mention, the natural position of the mollusk is to repose upon 

 its back ; the lower valve of the shell is the dorsal valve, and the 

 upper or ventral valve, from which anchorage is obtained, pro- 

 jects over one side, like a beak, for lowering the tendons. In 

 Crania the position of the mollusk is reversed j the ventral valve 

 is undermost, and, having no need, or even space, for a tendinous 

 anchor, the valve becomes agglutinated at once to the place of 

 attachment. It will be observed that in the genus Orhicula the 

 shell is not so closely adherent, and there is a tendinous muscle 

 of attachment passing through a fissure in a disk of the under 

 valve; and it has been conjectured that the same thing obtains 

 in a rudimentary form in Crania, in an early stage of its deve- 

 lopment. The arms or brachial appendages of Crania have no 

 internal apophysary skeleton for their support. They are folded 

 into a pair of spiral coils, which are directed towards the con- 

 cavity of the upper valve, and supported there by a central pro- 

 minence, termed the rostellum, rising up between them from the 

 lower valve. This valve, as with other adherent shells, varies 

 considerably in thickness in different individuals of the same 

 species, according to the nature of its place of attachment. 



Synopsis of Species. 



1. Crania anomala, Miiller, Zool. Dan. vol. i. p. 14, pi. 5. figs. 1 

 to 7. 



Patella anomala, Miiller. 

 Anomia craniolaris pars, Linnseus. 

 Patella distorta, Montagu. 



