TRIMERELLIDA. 335 
C. Ignabergensis is equivalve, and either quite free or very 
slightly attached. C. anomala, Mull. (exxxix, 72-75), is grega- 
rious on rocks and stones in deep water, both in the North 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- 
erania, Hichw., 1871.) Is free and has the internal border of the 
valves smooth; the branchial impressions blend in front. C. 
antiquissima, Kichw. 
CRANISCUS, Dall, 1871. (Siphonaria, Quenst., non Sowb.) 
Fixed valve divided by a transverse and a longitudinal median 
septum into three cells, the posterior of which contains the mus- 
cular impression and the rostrellum. C. velata, Quenst. (Cxxxix, 
TOy TT): 
ANCISTROCRANIA, Dall, 1877. (Cranopsis, Dall, non Adams, 
1871.) Shell attached, upper valve with two slender pointed 
apophyses divaricating ‘from the internal apex of the upper valve. 
C. Parisiensis, Defrance (¢xxxix, 78-80.) Cretaceous. 
SPONDYLOBOLUS, M’Coy, 1852. (Spondylobus, Davidson, 1853.) 
Suborbicular, slightly narrowed towards the short, indistinct 
hinge-line; nearly equivalve, flattened; hzemal valve with a 
slightly excentric 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, minutely fibrous. C. 
craniolaris, M’Coy. L. Silurian; Ireland. 
Famity TRIMERELLID A. 
Usually massive; umbo of the large valve often large, pointed, 
solid or hollow, ite 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 
erescent 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. 
