320 BALANIDJE. 



for analogy would have made me believe that this species 

 must have been imbedded in some sponge-like body, such as 

 the bark of a zoophyte, and that it could not have lived 

 unattached. I may add that a small fragment of a brown 

 leathery substance adhered to the upper end of one of the 

 two specimens, and this seems to indicate attachment. 



General Appearance. — Shell shaped like a pointed acorn ; slightly- 

 flattened ; orifice extremely small; surface very finely punctured, 

 covered by a purplish-brown epidermis, with transverse stripes of dif- 

 ferent shades, and with the apex dark ; according to Mr. Dana, when 

 fresh, the colour was purplish-carmine. Radii narrow, white. The 

 carino-lateral compartments are extremely narrow ; the wall-portion 

 (fig. 9 b) forming a mere linear rib, terminating downwards in a sharp 

 point, which does not reach the basal cup : hence this compartment 

 evidently tends to become rudimentary. The basal cup is moderately 

 deep and pointed. Basal diameter '1(3; height, from the bottom of 

 the cup to the top of the shell, "24 of an inch. 



Scuta : narrow, with the upper part produced ; not striated longi- 

 tudinally ; coloured by a pale purple, longitudinal band. Internally, 

 there is scarcely a trace of an articular ridge, which, in the other 

 species, is always more or less developed. Tergu with the spur bluntly 

 pointed ; nearly the whole basal margin, on the carinal side, slopes 

 towards the spur. 



Internal Structure of the Parieles, Radii, and Basal Cup. — The 

 parietes are strongly ribbed internally ; and these ribs are connected by 

 very narrow, less prominent, transverse, slightly branched ridges, giving 

 a reticulated structure to the inner surface. Between several of the 

 main longitudinal ribs, in the lower part of the shell, new ribs may be 

 seen in process of formation, and these tend to convert the reticulated 

 structure into a double row of minute cells. I have not met with an 

 exactly similar structure in any other cirripede ; but I have no doubt 

 that the little transverse ridges are homologous with the transverse cal- 

 careous septa in the parietal pores of many Balani, in the same manner 

 as the internal longitudinal ribs, in this and other species of Acasta, are 

 homologous with the longitudinal septa forming the above pores. The 

 edge of the basal cup is pectinated with teeth, which lock into the 

 teeth formed by the ends of the internal parietal ribs. The radii are 

 narrow, and have smooth edges. The alse project beyond the parietes 

 to a remarkably small extent. The sheath is free, or hollow beneath. I 

 have already described the almost rudimentary condition of the carino- 

 lateral compartments ; this is best exhibited in an internal view of the 

 two compartments, as given in PI. 9, fig. 9 b. 



Animal" s body unknown to me : from Mr. Dana's drawing the three 

 posterior pairs of cirri seem to have been much elongated : and the 

 rami of the first pair, as usual, unequal in length. 



M. Deshayes has given an indifferent figure and imper- 

 fect description ot Acasta tubulosa (Guerin, Magasin de 



