TRIMERELLID^. 335 



C. Tgnabergensis is equivalve, and either quite free or very 

 slightly attached. C. anomala, Miill. (cxxxix, 72-75), is grega- 

 rious on rocks and stones in deep water, both in the Noi'th Sea 

 and Mediterranean ; the animal is orange-colored, and its labial 

 arms are thick, fringed with cirri, and disposed in a few hori- 

 zontal gyrations. 



PSEUDOCRANiA, M'Coy, 1859. (Pholidops, Hall, 1860. Paleo- 

 crauia, Eichw., 1871.) Is free and has the internal border of the 

 valves smooth ; the branchial impressions blend in front. G. 

 antiquissima^ Eichw, 



CRANiscus, Dall, 1871. (Siphonaria, Quenst., non Sowb.) 

 Fixed valve divided b}^ a transverse and a longitudinal median 

 septum into three cells, the posterior of which contains the mus- 

 cular impression and the rostrellnm. C. velata, Quenst. (cxxxix, 

 76, 77). 



ANCiSTROCRANiA, Dall, 1877. (Cranopsis, Dall, non Adams, 

 1871.) Shell attached, upper valve with two slender pointed 

 apoph3'ses divaricating from the internal apex of the upper valve. 

 C. Farisiensis, Defrance (cxxxix, 78-80.) Cretaceous. 



SPONDYLOBOLUS, M'Coy, 1852. (Spondylobus, Davidson, 1853.) 

 Suborbicular, slightly narrowed towards the short, indistinct 

 hinge-line; nearly equivalve, flattened; haemal valve with a 

 slightly excenti'ic apex, beneath which, on the interior the sub- 

 stance of the valve is thickened into a wide undefined boss ; 

 opposite valve slightly longer, from the apex being perfectly 

 margined and somewhat produced ; channeled by a narrow trian- 

 gular groove, the anterior end of which is flanked within by two 

 very prominent thick conical shelly bosses, representing hinge- 

 teeth ; valves thick, testaceous, not glossy, minutelj^ fibrous. G. 

 craniolaris, M'Coy. L. Silurian ; Ireland. 



Family TRIMERELLID^. 



Usually massive; umbo of the large valve often large, pointed, 

 solid or hollow, its hinge-face with a well-developed area, and 

 large deltidium, solid throughout; hinge of both valves rudely 

 or faintly dentary ; that of the pedicel-valve thick, entire, some- 

 what elevated, sometimes supported by an upright rib, with a 

 wide median space enclosing a lozenge-shaped scar ; that of the 

 brachial valve with a more or less elevated median prominence, 

 or depression ; attached to the interior surface of the posterior 

 half of both valves is an elevated platform, solid, or doubly 

 vaulted ; from the middle of its anterior end a median plate 

 occasionally projects into the anterior half of the valve, especially 

 the brachial one ; both valves have a profound impression or 

 crescent running a little within the margins of their posterior 

 half, including the hinge ; a submarginal impression or archlet 

 characterizes the anterior half of the valves. 



