384 BALANIDjfc. 



symmetrically, the rostrum and carina not exactly facing each 

 other.* The shell, though so thick and massive, yields easily 

 along the lines of suture. The radii are moderately wide, 

 or narrow, or not at all developed, being represented by 

 mere sutures: in this latter case, in C. caretta, the orifice 

 of the shell is enlarged, in the same manner as we have 

 seen in some species of Balanus and Tetraclita, by the 

 gradual wearing away of the upper part of the shell. In 

 C. testudinaria, the radii have a singular notched structure 

 (fig. 1 a), and the whole shell a star-like appearance. The 

 orifice is not filled up by the elongated opercular valves, — 

 a considerable extent of opercular membrane being visible 

 on the two sides. The largest specimen which I have seen, 

 namely, of C. testudinaria, was nearly two and a half inches 

 in its longer diameter. 



Structure of the Parietes. — The parietes are of unequalled 

 thickness, especially in the first two species of the genus. 

 From the outer lamina (see PI. 14, fig. 4, and the section 

 in PL 15, fig. 1), numerous vertical plates extend inwards, 

 alternately to a less or greater distance, some of them reaching 

 to the inner lamina : these answer to the longitudinal pa- 

 rietal septa in other genera, and the elongated cavities 

 between them (which occur in C. testudinaria and patula) 

 answer to the parietal tubes or pores. The radiating 

 plates or septa have their sides finely channelled, and their 

 basal edges generally slightly sinuous and always finely 

 toothed. The interspaces between the plates in the upper- 

 most part of the shell are filled up solidly, and, in C. caretta, 

 even down to near the basis : in this latter species, the 

 plates are irregular and much broken up, so as in parts to 

 consist of little, separate, flattened points. In C. patula, 

 the inner lamina of the parietes (b, in fig. 4. PL 14) can be 

 best made out to be distinct from the sheath {ece in fig. 4, 

 and d in the section of C. testudinaria, fig. 1, PL 15). The 

 sheath in this genus descends in a very remarkable manner 

 to the basal membrane, and has its basal edge toothed like 

 the basal edges of the radiating septa. The inner lamina 



* In Mr. Stutchbury's collection there is a specimen of C. testudinaria in 

 which there are only five compartments, one of the lateral compartments having 

 been aborted; of this I have seen no other instance in any genus. 



