378 BALANID.E. 



tergum is very much narrower, with the spur sharper, so that at first I 

 concluded that these two sub-varieties were specifically distinct : we shall, 

 however, soon see in var. 2 and in var. 4, that no confidence whatever 

 can be placed in the exact breadth of the tergura, or in the porosity of 

 the walls ; hence I have been driven to consider the two varieties just 

 mentioned as merely sub-varieties. 



Var. (2), fig. 6 e, 6f, 6g. — Hab. China; Red Sea. — The shell is 

 almost invariably permeated by pores, sometimes arranged in two or 

 three very irregular rows. In some specimens the scutum exactly re- 

 sembles that in var. 1, but with the tooth near the rostral angle often 

 rather larger : in other specimens the scutum is much more elongated 

 transversely (fig. 6 e), with the adductor ridge more medial, and the 

 basal margin not at all hollowed out at the basi-tergal corner of the 

 valve. The tergum, here, is the remarkable feature, being sometimes 

 excessively narrow, with a long sharp spur, which often, but not always, 

 terminates in a needle-like point. In other specimens, from the same 

 coral and certainly belonging to this same variety, the valve is not so 

 narrow (6/7), and the spur not so pointed ; consequently (as in several 

 analogous cases in other cirripedes) it is impossible to draw any line of 

 distinction between the specimens with the narrow and broad terga. 



Var. (3), fig. 6h [Creusia grey aria of G. B. Sower by /] — Hab. Un- 

 known. — The scutum presents here exactly the same considerable range 

 of variation as in var. 2. The tergum is broad, as in var. 1, but the 

 spur is rounded, and from not being placed so immediately close to the 

 basi-scutal angle of the valve, gives to it a rather different aspect. The 

 breadth of the spur varies ; an extreme variety is given in fig. 6 h. 



Var, (4), PL 14, fig. 6 i, 6 k, 61. — Hub. Philippine Archipelago; 

 West Indies. — The scutum here presents the same sub-varieties as here- 

 tofore, excepting that I have not seen any so much elongated trans- 

 versely. The shell is covered either with slight, closely approximate 

 ribs, as in the foregoing varieties, or with more distant and more 

 prominent ribs. In specimens taken out of the same branch of coral 

 the walls were either porose or solid. Sometimes the sheath is bright 

 purplish-pink. It is the tergum, again, which presents a remarkable 

 range of difference; for the longitudinal depression or furrow which 

 in the former varieties was quite open, here has its edges more or less 

 folded inwards, and is sometimes quite closed. This same variation 

 has been commonly observed in many species of Balanus, in which it 

 appears to be dependent on the age of the individual ; but this does not 

 appear to be the case in the present genus. As a consequence of the 

 greater or less folding in of the two sides of the furrow, the spur is 

 rendered more or less narrow and pointed, and thus becomes removed 

 to a greater or less distance from the basi-scutal angle of the valve. 

 Further, as a consequence of this folding in, the internal surface of the 

 valve along the line of the external furrow, is raised into a longitudinal 

 ridge. The length of the spur varies considerably. In some very 

 young individuals, the basal margin descends lower on the scutal than 

 on the carinal side of the spur. In one set of specimens (fig. 61), a 

 plate extended from the carinal margin to near the central longitudinal 

 ridge just mentioned: a similar structure was described under Pyryoma 

 cancellatum. 



