34 FOSSIL C1RRIPEDIA. 



elongated, attached to Sponges, or rarely to the bark of Isis : scutum and tergum articulated 

 together, subtriangular. 



Under the last genus, I have made a few remarks on the close affinities of this sub-genus 

 to Balanus, and have given my reasons for retaining it, so that I need not here 

 repeat them. 



Acasta undulata. Tab. II, fig. 6a — 6/ 



A. testa, ad speciem, ut in " A. spongites," sed majore : scuto externe striis longitudi- 

 nalibus, sape binis, signato, sulcis intermediis latioribus .- tergi calcare, pane ^ valva 

 latitudine. 



Shell, apparently, as in A. spongites, but larger : scutum marked by longitudinal ridges, 

 often in pairs, with the intermediate furrows rather wide : spur of tergum nearly half as 

 wide as valve. 



Fossil in Coralline Crag (Sutton), Mus. S. Wood, Bowerbank. 



I owe to Mr. Wood the inspection of a fine suite of valves, which, though separate, I 

 have no reason to doubt have all been rightly attributed to the same species. Owing to the 

 shell never having been found entire, its general shape is not known, and, what is of more 

 consequence, the relative proportional width of the parietes of the carino-lateral compart- 

 ment is unknown. I have (but with doubt) given it a distinct specific name, owing to the 

 peculiar character of the furrows on the scuta, and to the large size of the whole shell. In 

 its other characters it comes nearest to A. spongites, excepting in the spur of the tergum, 

 which resembles that of A. sulcata. 



The external surfaces of the compartments appear generally to have been smooth ; but 

 in several specimens they are studded with the sharp shelly points so common in the 

 genus. A rostrum (Tab. II, fig. 6a), and lateral compartment (fig. 6b), have been figured. 

 The radii are not wide. The basis (fig. 6c) is cup-formed : its edge is either quite smooth, 

 or is very finely crenated. The basis is sometimes quite irregularly perforated, as in the case 

 of several recent species, by numerous minute orifices, which, when the animal was 

 alive, no doubt were covered by membrane. Internally the parietes are feebly ribbed, as 

 in A. spongites. Judging from the dimensions of the separated valves, this species must 

 have equalled and perhaps exceeded in size the largest living species, namely, A.glans, from 

 Australia. Hence we may infer, that the basal diameter probably exceeded '55 of an 

 inch -. I may add, that the largest European specimens of A. spongites, from Naples and 

 Portugal, are only 3 of an inch in basal diameter. 



Scuta (fig. 6e). — These seem to resemble the scuta of A. spongites in all respects, except 



