PENTELASMIS 



country^ but are common everywhere. Several are found 

 on our coasts^ affixed by the base of their peduncles to 

 sea-weeds, pieces of timber, the bottoms of shipping, &c. 

 upon which they seem to increase very rapidly. Its shell 

 consisting of only five pieces, may be considered as quite 

 sufficient to distinguish it from Hepielasmis, Leach, which 

 has seven pieces; from Scalpellum, Leach, which has thir- 

 teen pieces; and from PoUicipes, Leach, which has an 

 indefinite number of pieces. 



Fossil specimens of this Genus are exceedingly un- 

 common ; we have never seen anything but fragments 

 from two beds, viz. the Calcaire grossier of Grignon, and 

 the Suffolk Crag. There is, however, a fossil not unfre- 

 quently found in the Lithographic stone of Solenhofen in 

 Germany, which has been referred to this Genus ; never- 

 theless, from an attentive consideration and comparison' 

 of its structure with that of other palates^ we are con- 

 vinced that it is not a Pentelasmis, but part of the palatal 

 bones of a fish. 



We believe all the genera composing the two families 

 of Balanidai and Pentelasmidae to be strictly marine. 



The shells of this Genus are all thin, and their mem- 

 braneous integuments are open in front for the passage of 

 numerous fringed tentacula, which, when the animal is 

 alive in the sea water, are frequently in motion, as if in- 

 tended to cause a current of water containing its prey to 

 descend towards its mouth. Lamarck, observing certain 

 characters in which these animals accord either with his 

 Brachiopoda or the Crustacea, seems, however, to consi- 

 der them as perfectly distinct; we venture, nevertheless, 

 a hint drawn from the consideration of several analogies 

 in the structure of various parts, that they may be 

 regarded as an intermediate class of beings between the 

 two above-mentioned. This, however, is only intended 

 as a hint to draw the attention of naturalists who have 

 good opportunities of observing them all in their living 

 state. 



We have represented at 



Fig. !• Pentelasmis Isevis. 



2. The valves of the same open and detached, to show their shape and 

 disposition with respect to each other. 



