NOMENCLATURE OF THE SHELL OF A SESSILE CIRRIPEDE.

[Illustration: SHELL. Fig. 1.

_Orifice_ of shell, surrounded by the _sheath_. _Sheath_ formed by the

_alæ_ (_a_--_a_.) and by portions of the upper and inner surfaces of

the _parietes_ (_p_--_p_.)

N.B. In Balanus, and many other genera, the Rostrum and Rostro-lateral

compartments are confluent, and hence the Rostrum has the structure of

Fig. 2.]