Professor MacGillivray on the Cirripedia. 179 



four calcareous pieces, forming two lateral and terminal valves ; the 

 anterior plates triangular, oblique, externally concave, very acute, trans- 

 versely grooved, their posterior margins longitudinally cleft ; the pos- 

 terior plates triangular, incurvate, the base with a narrow process, 

 from which a longitudinal groove runs to the apex, the anterior margins 

 with a shallow groove, and a strong ridge ; the free margins of these 

 opercular valves denticulate. 



Coronary tube or shell conical, somewhat oblique, and obliquely trun- 

 cate, of six united pieces, forming six elevated ridged areas, and six de- 

 pressed narrow areas, which are white, flat, glossy, distinctly striulate 

 transversely and longitudinall}', often with some deep transverse grooves. 

 The anterior or ventral elevated areas with about five ribs, and several 

 smaller; the ventro-lateral with four or live, and some smaller; the 

 posterior-lateral with one or two ; the posterior with five or more ; the 

 ribs straight, compressed, narrow, obtuse, slightly rugose, leaving the 

 base-line crenate; their intervals obscurely striated, and covered with 

 a greyish-brown, or brownish, or purplish-red epidermis. The shell 

 white, or tinged with purple or pink, sometimes in irregular transverse 

 bands. 



The accessory or internal shell or tube extends balfway down, and 13 

 composed of six imbricated thin plates, glossy internally, with faint 

 transverse stride. Beyond it the tubo is longitudinally grooved on the 

 inner surface, and closed below by a calcareous plate, which is diver- 

 gently- striate. The walls of the tube have numerous narrow, compressed 

 cells, separated by very thin partitions, from the base to the apex of the 

 elevated areas. They are filled with a pulpy cellular tissue, which com- 

 municates with the mantle by small apertures at the junction of the 

 basal plate with the shell internally. The articular margins of the six 

 pieces of the shell are transversely grooved. 



I have traced it down to the size of one-twelfth of an inch in diame- 

 ter. It has then a very different appearance ; being couical, white, 

 with six plates, of which the summits are obtuse in outline, but thin- 

 edged, and separated from each other, leaving an ovato-pentagonal 

 aperture, about a third in width of the diameter of the base; the ele- 

 vated areas slightly and irregularly longitudinally rugose ; the depressed 

 areas very narrow, glossy, and transversely striulate. In this state they 

 are found solitarily, or crowded on the wood in chinks of the pitch, or 

 sometimes upon the pitch itself, or upon the tegmen of the Otion, ia 

 which latter situation, however, they do not attain the diameter of a 

 quarter of an inch before they fall off. As they enlarge, the elevated 

 areas become more rugose, and the tips of the plates become broken; 

 and when their diameter at the base is about two-twelfths of an inch, 

 the strong, prominent ribs begin to be formed. When full-grown, they 

 always have the tips broken or worn off, in various degrees, and the 

 margin of the aperture continuous. As the base continues adherent to 

 the wood, and enlarges in diameter, the shell insinuates itself beneath 

 the pitch, raising it up so as to form a general coating, broken or conti- 

 nuous, from which, up to a considerable size, the aperture only is seen 

 projecting. 



It is scarcely probable that this species has not been described; 

 but I am unable to trace it in any work accessible to me. One of 

 the first English nialacologists of the present day, informs me, that 

 he has it in his cabinet marked Balanus porcatus, altliough he does 

 not know on what authority. Wiiothjr that be the true name or 

 not, it will answer our purpose equally well, it not being my object 



