A manual of the Mollusca, or, A rudimentary treatise of recent and fossil shells . ted, in all probabi-lity, by these dorsal arms. In one group (arietes,)the operculum consists of a single piece, and is hornyand flexible.! Iji the round-backed ammonites theoperculum is sheUy, and divided into two plates by astraight median suture (fig. 42). They were de-scribed in 1811, by Parkinson, who called them tri-gonellites, and pointed out the resemblance of their Fig- * Fig. 40. Gomphoceras Bohemicum (Barrande), reduced view of the aperture ; s,the siphonal opening. Fig. 41. phragmoceras callistoma (B
A manual of the Mollusca, or, A rudimentary treatise of recent and fossil shells . ted, in all probabi-lity, by these dorsal arms. In one group (arietes,)the operculum consists of a single piece, and is hornyand flexible.! Iji the round-backed ammonites theoperculum is sheUy, and divided into two plates by astraight median suture (fig. 42). They were de-scribed in 1811, by Parkinson, who called them tri-gonellites, and pointed out the resemblance of their Fig- * Fig. 40. Gomphoceras Bohemicum (Barrande), reduced view of the aperture ; s,the siphonal opening. Fig. 41. phragmoceras callistoma (Barr.) both from the , Bohemia. t This form was discovered by the late Miss Mary Anning, the indefatigable col-rector of the lias fossils of Lyme Regis, and described by Mr. Strickland, Geol. Journal,vol. I., p. 232. Also by M. Voltz, Mem. de IInstitute, 1837, p. 48. I Trigonellites lamellosus, Park. Oxford clay, Solenhofen (and Chippenham,) as-sociated with ammonites lingulatus, Quenstedt. (= A. Brightii, Pratt). From a speci-men in the cabinet of Charles Stokes, CEPHALOPODA. 81 internal structure to tlie cancellated tissue of bones. Their external siurface issmooth or sculptured ; the inner side is marked by lines of gron-th. Forty-five kinds are enmnerated by Bronn ; they occur in aU the strata in whichajumonites are found, and a single specimen has been ligm-ed by M. DArcliiac,from the Devonian rocks of the Eifel, where it was associated with goniaiites* Calcarious mandibles or rhyncholites (F. Biguet) have been obtained fiomaU the strata in which nautili occm; and from their raiity, their laige sizeand close resemblance to the mandibles of the recent nautilus, it is probablethat they belonged only to that In the Muschelkalk of Bavai-ia onenautilus [N. arietis, Keinecke, = N. bidorsatus, Schlotheim,) is found, and twokinds of rhyncholite; one sort, coiTesponding \\ith the upper mandible of therecent nautilus, has been called rhyncholites hirundo (pi.
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectmollusks, bookyear185
