BIVALVIA. 91 
and it imparts a gloss or polish to the exterior like that of 4. Zwcida. The dental area of 
our shell appears to be well furnished with teeth, and there is a slight sinuation in the 
ventral margin. 
16. Arca TESSELLATA, Fisher, MS. Tab. XV, fig. 14, a, 0. 
Spec. Char. A. testdé crassd, elongata, ovato-oblongd, depressd, sub-obliqud, inequi- 
laterali ; siphoni-regione angulo decurrente definitd ; sulcis quatuor crassis, granosis ornata ; 
umbonibus depressis, obliquis; ared connexiis obliqud, sulcatd, ared cardinali arcuatd tn 
medio edentuld, ad extremitatem pauci-dentata ; margine ventral sinuoso, integro. 
Shell elongate, of an ovately oblong form, depressed, slightly oblique, inequilateral ; 
siphonal region with an angular elevation, ornamented with four thick rays; beaks 
depressed, oblique ; area of connector narrow, oblique, and ridged angularly; dental area 
slightly curved, with few teeth at the extremities, central portion plain; ventral margin 
sinuated, edges plain. 
Length, \% inch; height, :ths of an inch. 
Localities. Brook (Fisher), Huntingbridge (Ldwards). 
This appears to be closely related to two or three species found in the Paris Basin, but 
with no one of which does it accord so as to be satisfactorily regarded as anidentity. It is 
not far removed from A. rudis, Desh. (‘ Coq. foss. des Env. de Par.,’ t. 1, p. 210, pl. 33, 
figs. 7, 8), but the rays and decussating ridges of that species are larger and coarser than 
they are on our shell, and the dental area is different. 4. Morzerz, Desh. (‘ An. vert. du 
Bass. de Par.,’ p. 874, pl. 65, figs. 18, 19), also resembles our shell, but it has a less pro- 
minent and less distinctly marked angular ridge, running from the umbo diagonally across 
the siphonal region. The rays which ornament our shell are broad and flat, separated by 
a deep and narrow depressed line, decussated by distinct lines of growth, which imbricate 
the rays on the larger side. ‘The adductor-muscle-marks are large, particularly the oral 
one, and the mantle-mark is not very near to the margin of the shell ; there is also a long 
pedal-muscle-mark under the dental margin on the siphonal side. The teeth of our speci- 
mens are not in very good condition, but they appear to have been numerous, and those 
on the pedal side are slightly inclined. ‘There is a sinus or indenture in the margin for a 
byssus, and the siphonal region is broader or higher than on the pedal side. 
A fossil apparently identical with this species has recently been obtained at Lattorf, 
Magdeburgh, by Herr A. von Koenen, in a deposit of the Upper Eocene (or in what is 
called by the German geologists Oligocene) period. The German specimens are, however, 
much larger than our own. One perfect individual measures three and a half inches, and 
a fragment of the same species indicates a length of nearly five inches. 
13 
