BALANUS. 29 



radiating ridges : the septa between the radiating pores are themselves often in part porose, 

 as was plainly the case in the specimen (fig. 3b) engraved. The orifice of the shell is 

 large and elongated in its rostro-carinal axis, especially in yonng specimens. The basal 

 diameter of the largest specimen is '4 of an inch. 



The scuta (fig. 3c) have no trace of the two or three longitudinal furrows so con- 

 spicuous on these valves in B. bisulcatus, and which, in that species, run down to the basal 

 margin from the apex of the valve, this fact showing that the furrows occur in quite young 

 individuals. The whole valve is not quite so narrow as in B. bisulcatus, but otherwise 

 agrees with it in shape : internally, there is hardly any difference ; but the articular furrow is 

 not quite so wide : the articular ridge is very prominent, and abruptly truncated at its lower 

 end : the adductor ridge is also prominent • it here runs a little higher up the valve than 

 in B. bisulcatus. The tergum (fig. 3d) differs more in the two species : the spur is not so 

 broad ; measured in its upper part, it is only about one third of the entire width of the 

 valve, instead of being half as wide as the valve : it is considerably longer, depending 

 beneath the basi-scutal angle more than half its own width : the basal margin of the valve 

 on the carinal side, does not slope so gradually into the spur ; the occludent and carinal 

 margins are slightly arched, as in B. bisulcatus. Internally, the surface is rough, the 

 articular ridge is prominent, and the crests for the tergal depressores are well developed, — 

 all as in B. bisulcatus. It is remarkable how generally the opercular valves have been 

 preserved in this species in its fossil condition, as compared with most other species of the 

 genus-. 



It is not easy to distinguish, by external characters, the rugged varieties of this species 

 from B. crenatus; indeed, the only difference is that the furrows receiving the edges of the 

 radii, generally, exhibit in B. crenatus slight impressions of the septa, which are entirely 

 absent in B. dolosus. By internal characters, such as the non-porose parietes, and porose 

 basis, our present species widely differs from B. crenatus. 



10. Balanus unguiformis. Tab. II, fig. 4a — 4/. 



Balanus unguiformis. J. de C. Sowerby (!) Mineral Conchology (sine descriptione), 



Tab. 648, fig. 1, (Jan. 1846.) 

 . — erisma. J. de C. Sowerby (!) lb., fig. 2. 



— perplexus. Nyst, apud D'Omalius (sine descript. vel Tab.), G6ologie de la 

 Belgique, 18.53. 1 



B. parietibus tenuibus, interdum poris perforatis ■■ radiis sine poris, marginibus su- 

 perioribus obliquis ; aciebus suturalibus tenuissime crenatis .• basi sine poris : tergi calcare 

 angusto, obtuso. 



1 I am much indebted to M. Bosquet for specimens bearing this title, from Klein Spauwen, which 

 certainly appear to me, as far as can be judged by the separated compartments, without the opercular valves, 

 to belong to our present species. 



