198 PERMIAN FOSSILS. 
the pallial line is even less inflected than it is in 4. elegans, the species just referred to. 
The low or proximo-ventral position of the anterior adductor muscular impressions, 
which is striking compared with the position of the same impressions in M/ya, Lutraria, 
Panopea, and some other genera, appears to be indicative of Ad/orisma having been 
more a surface-creeping, than a decidedly burrowing genus. That the position of the 
anterior adductor muscle is influenced by the terebrating habits of the mollusk, is 
strongly evidenced by the fact, that in the decidedly burrowing genera, Pholas, Teredo, 
and Xylophaga, this muscle is situated considerably above its usual situation,—so high in 
some, that the surfaces to which it is attached, or the anterio-cardinal margins of the 
valves, project externally in front of the umbones, and are even insome species, such as 
Pholas dactylus and P. candida, reflected considerably over them. Zhracia pubescens has the 
anterior adductor muscular impressions as low as in A//orisma. Perhaps the foregoing 
observations may induce those, possessing the opportunity, to endeavour to ascertain 
if the habit of this species is confirmatory of the view herein taken of that of A/orisma.’ 
The present genus, supposing the so-called Pholadomya Munsteri, D’Archiac and 
De Verneuil, to be a species, is not known to occur in earlier than the Devonian rocks : 
it is rather common in the Carboniferous ; meagrely represented, at least as far as is 
known, in the Permian; and anything but abundant, taking M/yacites to be the same, 
in the Triassic deposits. I have not yet been able to satisfy myself of its existence in 
any rocks of a later age. 
ALLORISMA ELEGANS, King. Plate XVI, figs. 3, 4, 5. 
ALLORISMA ELEGANS, King. De Verneuil, Bull. Soc. Geol. de France, 2” série, t. i, p. 30, 
1844. 
a — », Ann. and Mag. Nat. Hist., vol. xiv, p. 316, 1844. 
— — », Geol. Russ., vol. i, p. 223, 1845. 
(?) AMPHIDESMA LUNULATA, Keyserling. Petschora-land, p. 258, pl. xi, fig. 16, 1846. 
(?) CYPRICARDIA BICARINATA _,, Op. cit., p. 257, pl. x, fig. 17. 
ALLORISMA ELEGANS, King. Tennant, Strat. List, p. 88, 1847. 
— — » Catalogue, p. 12, 1848. 
SANGUINOLITES ELEGANS, King. Howse, Trans. T. N. F. C., vol. i, p. 243, 1848. 
PaNOPMA LUNULATA, Keyserling. Geinitz, Versteinerungen, p. 8, pl. iii, figs. 21-2, 1848. 
Diagnosis.—* Form very inequilateral: doth ends closed; anterior one the shortest, 
and oblique superiorly ; posterior one rather square : wmbones somewhat gibbous : dorsal 
slopes with a faint angle running from the umbone to the posterior end of the shell: 
surface slightly wrinkled transversely, and crowded with minute pimples: pad/al sinus 
somewhat shallow.” (King.)” 
1 [have seen several hundred specimens of Allorisma sulcata in situ, that is, in a bed of shale in Redesdale ; 
but I have never seen any in an upright or inclined position, so as to indicate that they were a burrowing 
species. 
2 Catalogue, p. 12. 
