ANIMALS. 163 
differ remarkably in the position of their cartilage fulcra, which in the former are 
lamelliform, elongated in the direction of the cardinal line, and, as in Lutraria elliptica, 
directed downwards within the dorsal cavity (vide Pl. XX, figs. 2a, 3, 4); while in the 
latter they are external, and of the ordmary form. On examining another species 
somewhat resembling them, and which I provisionally named Alorisma constricta, the 
cartilage fulcra appeared to occupy an intermediate position. Hence I was led to 
consider that these shells were furnished with cartilage fulcra, varying from an internal 
to an external position ; and that they constituted a generic group, for which I proposed 
the name A/lorisma. Moreover, I predicated of the genus a character which was dis- 
played on several of my specimens of the so-called Miatella sulcata, viz. a sinus in the 
pallial line (vide Pl. XX, fig. 5c). It happens, however, that the last noticed character 
was based on insufficient data; that, in fact, the pallial line, which I had not then seen, 
of Sanguinolaria sulcata is entire, or, in other words, not sinuated, as was subsequently 
pointed out by Mr. Morris.? At the time this gentleman’s discovery was published, I 
ascertained that the [socardia unioniformis, Phillips, possessed a pair of cartilage fulcra, 
similar to those of Sanguinolaria sulcata, and an entire pallial line :* this led me to the con- 
sideration of De Koninck’s genus Hidmondia, which is typified with the former species. 
I now ascertained that Dr. Koninck had anticipated me in the discovery of the 
vertical cartilage fulcra, which he describes singly as “une lamelle transverse, étroite, 
profondément situee et en partie recouverte par le crochet et ayant probablement 
servi & supporter un ligament interne, d’une forme a peu pres analogue.” It will thus 
be evident, that in constructing the genus A//orisma, I have erred in placing together 
two widely-different kinds of shells,—the one (with the sinuated pallial line) having been 
inhabited by a mollusk with an anal and a branchial siphon,—the other (with the entire 
pallial line), by a mollusk unprovided with these appendages. It is equally evident, 
as regards the latter kind, the one represented by Sanguinolaria sulcata, that the 
—a character which was noticed in my paper (p. 316). This suspicion is now confirmed by the following 
extract from a letter with which I have been favoured by Dr. Fleming, to whom I forwarded a couple of 
specimens of this shell for comparison: “two of the shells do certainly resemble my Hiatella sulcata : 
on one of the casts there are traces of the strize, a character rarely to be met with owing to the extreme 
thinness of the shell, and its usual imperfectly preserved state.” 
' As this shell has apparently not been described, I venture to publish the following diagnosis of it. 
Allorisma constricta, King. Twice as wide as it is long. Umbones tumid; incurved ; approximating ; 
projecting behind the hinge ; situated a little behind the centre of the anterior half of the shell. Valves 
with a slight longitudinal constriction immediately in front of the umbones ; transversely ribbed ; marked 
with faint incremental lines. Ribs rather faint, and obliquely crossed with the incremental lines on the 
anterior third of the shell; dichotomised on the constriction; and rather prominent on the rest of the 
valves, except on their dorsal slope. Zunule oblong, and shallow. Corselet long, and rather deep. Dorsal 
line slightly concave ; ventral, flatly convex; anterior, evenly rounded ; posterior, obliquely rounded. 
Pallial muscular sinus shallow. Found in the Carboniferous shales, Redesdale, Northumberland. My 
largest specimen is two inches and a half wide. 
* Strzelecki’s Physical Description of New South Wales, &c., p- 270. 
® Specimens of this shell, and other allied species, showing an entire pallial line, I first saw in the valuable 
ocal collection of carboniferous fossils belonging to the Rey. Mr. Jenkinson of Lowick, Northumberland. 
