456 Mr. G. B. Sowerby on Pcntatrematites 



Art. LXII. On Pentatrematites orbicularis, acuta, and 

 pentangularis. By G. B, Sowerby, F.L S.^ S^c. 



In two former papers* I have described what I suppose to constitute 

 eight distinct species of Pentatrematites. Three others having since been 

 discovered by Mr, Gilbertson, he was induced by the expressed wish of 

 some friends to science, to forward descriptions of and observations on 

 them for publication in this Journal. By some unaccountable accident 

 his paper has been mislaid, and it becomes necessary, in order to 

 complete the subject as fully as possible, that I should here add the 

 characters of these three species. And I beg permission to subjoin a 

 note or two which I find accompanying the drawings with which my 

 brother will illustrate this and the last-cited paper. 



The first of these notes is as follows, " the ambulacra are composed 

 " of two rows of bones placed in two furrows by the sides of an angular 

 " ridge, and so articulated as to leave a pore between each ; these bones 

 " often fall off: the pores continue into the edge of the furrows," 



The othernote is " there were two specimens of P. elliptica showing 

 * * pores for respiration in the ambulacra ; these pores are connected with 

 * ' passages that lead to what are called the ovaries." 



Pentatrematites orbicularis. 

 P. globosa, fere circularis. Scapulares mediocres, usque ad dimidium 

 altingentes, emarginationis interscapularis angulo obtusissimo. 

 Interscapulares majores. Ambulacra hnearia, angusta, ad basin 

 prominula. 



Tab. Suppl. XXXIII, fig. 5. 



Pentatrematites acuta. 

 P. pyriformis, pentagonalis, superne lata, infra attenuata. Ambulacra 

 brevia, lata, angulis superne conspicuis. 



* Vol, II., p. 313, and Vol. IV., p, 89. 



