Sea-Weeds, Shells and Fossils

by Peter Gray; B. B. Woodward

a. Asiphonida (Siphonless).

b. Siphonida Integro-pallialia (with Siphons).—Pallial-line entire.

c. Siphonida Sinu-pallialia (with Siphons).—Sinus in pallial-line.

Fig. 18. Trigonia margaritacea.

Fig. 17. Hinge-teeth of Arca barbata.

Division a.—Asiphonida—is next subdivided into—