CLEIDOTHiERUS. 



elongated testaceous appendage, in form resembling the 

 human clavicle ; as far as this character goes, connecting 

 the Chamacea? with the Myarite of Lamarck. 



Shell bivalve, somewhat pearly, inequivalve, involute, 

 attached by the outside of the larger valve. Hinge with a 

 small conical pointed tooth in the free valve, fitting into 

 a corresponding pit in the attached valve. A testaceous, 

 rather elongated, curved appendage,* connected by car- 

 tilage, is inserted into a deep cicatrix within each umbo. 

 Muscular impressions two in each valve, lateral, the ante- 

 rior ligulate, the posterior suborbicular. Muscular im- 

 pression of the mantle entire. Ligament external. 



The only species of this Genus at present known was 

 found attached to sandstone rocks at the entrance to Port 

 Jackson, by T. Young, Esq., R.N. Some imperfect speci- 

 mens had been sent to England many years ago, probably 

 from the same spot, by Mr. A.Humphrey. Some of these 

 have a brownish red colour, whereas those of Mr. Young 

 were of a dull livid colour. The imperfection of these 

 specimens consisted in their having lost the internal ap- 

 pendage. All the specimens have adhered by the anterior 

 side of the large and deeper valve. 



* Called by Mr. S. Stutchbury a clavicle." We do not approve of this 

 application of the term, because, though there is some analogy both in the form 

 and use between this appendage and the human clavicle, they are not cor- 

 responding parts of the animal frame. 



