. Zoology for high schools and colleges. Zoology. PTEROPODA. 239. — Siyllola vitrea.—After Verrill. A common form, occurring at the surface in harbors north of Cape Cod, as well as many miles ofE shore, is Spin- alis Gouldii Stimpson, the shell of which resembles a conical Helix. The largest form on the eastern coast of North America, extending from New York to the polar seas, is the beautiful Clione papillon- acea of Pallas, which has a head and lin- gual ribbon. It is rare on the coast of New England, but abundant from Labra- dor northward. "We have observed it rising and falling in the
. Zoology for high schools and colleges. Zoology. PTEROPODA. 239. — Siyllola vitrea.—After Verrill. A common form, occurring at the surface in harbors north of Cape Cod, as well as many miles ofE shore, is Spin- alis Gouldii Stimpson, the shell of which resembles a conical Helix. The largest form on the eastern coast of North America, extending from New York to the polar seas, is the beautiful Clione papillon- acea of Pallas, which has a head and lin- gual ribbon. It is rare on the coast of New England, but abundant from Labra- dor northward. "We have observed it rising and falling in the water between the floe-ice on the coast of Labrador. It is an inch long, the body fleshy, with no shell, the wings being rather small. The larvae of the Pteropods pass through a trochosphere stage, being, as in Cavolina, spherical, with a ciliated crown. It after- wards assumes a veliger form. Fig. 179 represents a worm- like, segmented, Pteropod larva, the adult of which is unknown. In other genera the larvae are annulated, resem- bling the larvae of Annelides. The Pteropods are, in some degree, a generalized type. They have a wide geographical distribution and a high antiquity; forms like Cavolina, viz.: Theca, Conularia, Tentaoulites, Cornulites, etc., dating back to the palaeozoic formation ; Theca-like forms {Pugiunculus and Hyolithes) occui'ring in the primordial rocks. Order 3. Gastropoda.—This great assemblage of mollusks is represented by the limpets, whelks (Figs. 180-183), snails, and slugs. The head is quite distinct, bearing one, and sometimes, as in the land-snails, two pairs of tentacles, with eyes either at the bases, or at the ends of the tentacles, or, as in Trivia californica (Pig. 184), they are situated on projections near the base of the tentacles. All the Gastropods move or glide over the surface by the broad creeping-disk, a modification of the foot of the clam, PiK. V pod larva. Ptero-. Please note that these images are extracted fro
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