OCR Text |
Show 1889.] SO-CALLED PHYSCE O F AUSTRALIA. 141 p. 139) with the same teeth of these Bulini will make this clear. In Planorbis the central tooth is broad-based, bicuspid, while the laterals are tricuspid ; in Limneea the central tooth is long and narrow, unicuspid, while the laterals are bicuspid. A Bulinus, therefore, is not so much a sinistral Limneea as a spiral Planorbis. Further research, as the animals of more species are investigated, may, perhaps, bring out some points of difference leading to division into subgenera of the Australian and Austro-Polynesian species. It is possible that the somewhat wing-shaped form of the central tooth in some cases (see figs. 2, 3, 5, 7, 8, p. 139), as compared with its more regularly square shape in others (see figs. 1 and 4), may indicate a basis of subdivision ; but at present there does not seem sufficient material to work upon. Finally, as regards nomenclature. Adanson, in 1757, described and figured1 under the name of Le Bulin or Bulinus a small sinistral freshwater shell from Senegal, length 1^ lines, breadth f line. The shell is evidently not adult, but the description and magnified drawing of the animal, which shows none of the produced mantle-lobes of a true Physa (indeed, Adanson fortunately remarks, " le manteau tapisse tout l'interieur de la coquille sans sortir au-dela des bords de son ouverture " ) , are sufficient to enable us to recognize it as belonging to the genus now under investigation. Fischer, therefore, is quite right in adopting Bulinus as the generic name2. Isidora (Ehrenb. 1831) is a synonym, see Jickeli, loc. supr. cit. Fischer, in his ' Manuel,' goes on to enumerate five subgenera, viz. Pyrgophysa, Plesiophysa, Ameria, Glyptophysa, and Physopsis. Pyrgophysa was proposed by Crosse3 for Ph. mariei, Crosse, from Nossi-Be, on the ground of its turreted spire. But this subgenus is of little value, as the Australian species present every variety of such formation. Crosse's description of the shell (" haud nitens, vestimento opaco induta") makes it plain that it belongs to this genus. Plesiophysa (Fischer, 1883) includes the remarkable Ph. striata, d'Orb., from Guadeloupe. This must be the ' Physa sp.' from Point a Pitre4, the radula of which is described by Bland and Binney5 as follows : - " Central tooth 5-cusped, central of these the largest; laterals 4-cusped, one inner, large, stout ; marginals a reproduction of the laterals." This description at once removes the species from 1 Senegal, pp. 5-7, pi. fig. G. ii. 2 Yet he remarks: "Etymologie inconnu." Adanson, however, I.e., seems to make it fairly clear when he says:-" Cette denomination m'a paru lui con-venir, parce que l'animal pendant sa vie nage presque continuellement a fleur d'eau, et qu'apres sa mort la coquille flotte comme une petite bulle d'air trans-parente." 3 Journ. de Conchyl. 3° s<§r. xix. 1879, pp. 208-209 ; xx. 1880, pp. 141-142, pi. iv. fig. 5. 4 Maze (Journ. de Conchyl. 3° ser. xxiii. 1883, pp. 30-31) records Plesiophysa striata from Point a Pitre. 5 " Note on a curious form of lingual dentition in Physa," Ann. Lye. N. H N. York, x. 1873, pp. 255-257, pi. xi. figs. 2, 3. |