ANIMALS. 155 
thus characterised in the shell next to be noticed, and which is commonly placed in 
the genus Avicula; on the contrary, it has a deep angular byssal notch (vide Pl. XIII, 
fig. 7a), a sub-triangular cartilage pit, and a single subcentral muscular impression 
(vide Pl. XIII, fig. 20 a),—characters which appear to approximate the genus, claiming 
it, to Pectenide. Perhaps the claiming genus is typical of an undescribed family, 
merging Pectenide into Aviculide. ‘This view is somewhat confirmed by the histology 
which Dr. Carpenter has described of a probably congeneric species, the Avicula 
cygnipes, Phillips, in which “ we find no trace of either the prismatic cellular substance 
or the nacre, which are characteristic of 4vicula; but we meet, on the other hand, 
with the coarsely-corrugated and somewhat tubular structure of the Pectenide.' I 
am not acquainted with the character of the cartilage-pit, and the muscular impressions 
of the shells, which Bronn, Minster, and Goldfuss have placed in d/onotis ; but as 
their external form closely resembles that of the fossils about to be introduced, I am 
induced to place it in this genus. 
MONOTIS SPELUNCARIA, Schlothem. Plate XIII, figs. 5 to 21. 
GRYPHITES SPELUNCARIUS, Schl. Akad. Minch., p. 30, pl. v, fig. 1 a, 4, c, 1816. 
= — »  Petrefactenkunde, p. 292, 1820. 
— — »  Boué, Edin. Phil. Journ., vol. xii, p. 144, 1825. 
Propuctus — »  Brongniart, Tab. de Ter., p. 425, 1829. 
AVICULA GRYPHAOIDES, J. de C. Sow. Trans. Geol. Soc. Lond., 2d series, vol. iii, p. 
119, 1829. 
— — Hy De la Beche, Geol. Man., p. 384, 1831; Germ. 
Transl., p. 459, 1832; 3d English ed., p. 
573, 1833. 
PRODUCTA SPELUNCARIA, Schl. Op. cit. 
—_ — »» » Phillips, Encye. Met., vol. iv, p. 617, 1834. 
AVICULA GRYPHOIDES, J. de O. Sow. Op. cit., p. 617, pl. iu, fig. 6 a, 6. 
—  SPELUNCARIA, Schl. Quenstedt, Wiegmann’s Archiv, p. 82, pl. i, fig. 1, vol. 
1, 1835; 
PropuctTa — », Thomson, Outlines Min. Geol. &c., vol. 1, p. 326, 1836. 
AVICULA GRYPHOIDES, J. de C. Sow. Op. cit., p. 318. 
— — if Phillips, Lardner’s Cycl., Geology, vol. i, p. 190, 
fig. 3, 1837. 
—_ SPELUNCARIA, Schl, Geinitz, Leonhard u. Bronn’s Neues Jahrbuch, p. 639, 
1841. 
— — » Morris, Catalogue, p. 107, 1843. 
= —- », Geinitz, Geea von Sachsen, p. 96, 1843. 
1 Report of the Fourteenth Meeting of the British Association, p. 20, 1844. A specimen of an allied 
species, Avicula longicostata, Stutchbury, in the Bristol Museum, possesses a single sub-central muscular 
impression, as in Monotis speluncaria. 
