REPORT (>N THE CIRRIPEDIA. 147 



and hardly distinguishable. Fifteen species (one new one, 

 /!< i In,, us tenuis, n. sp.). 



G. Parietes not permeated by pores. Radii wanting. Basis mem- 

 branous. Two species (1 lot h new, Balanus coi'olliformis, n. sp., 

 and Balanus hirsutus, n. sp.). 



Section A. Parietes, and basis, and radii permeated by pores. 

 Balanus tintinnabulum, Linn. sp. (PI. XIT. figs. 18, 10). 



Lcpas tintinnabulum, Linnreus, Systema Naturae, 1767. 

 Balanus tintinnabulum, Darwin, Balanidae, 1854, p. 194. 



According to Darwin tins is one of the most difficult and variable species in the whole 

 genus. Darwin, therefore, distinguishes eleven varieties ; he does not consider thi m as 

 so many different species, because by repeated and very close observation he became 

 convinced that the several points of difference by which each variety is characterised are 

 variable. 



The species is represented by two different forms in the collection made during; 

 the cruise of the Challenger. I will treat of them separately. The first must be con- 

 sidered as variety (l) communis. It is represented by two specimens of very great size ; 

 in the largest of the two the base measures 63 x 51 mm., the height 50 mm. ; the other 

 is only a little smaller. The surface is totally hidden by a thick layer of calcareous 

 substance; this sticks firmly to the surface; where it is taken away, the bluish-purple 

 colour of the original shell appears. 



The shape of the shell is tubulo-conical, the orifice is large, rounded, triangular, very 

 irregularly toothed. Surface longitudinally ribbed ; ribs rather strong and flexuous ; 

 radii transversely plaited in lines, slightly darker-coloured than the parietes. The 

 sheath is not distinctly coloured and very broad. The strength of the shell is so 

 considerable that it deserves the name of massive. 



Scuta and terga with prominent lines of growth. The ribs on the surface of the 

 scuta are finely toothed. The basi-tergal corner of the scutum is very much rounded off. 

 Articular ridge broad and much reflexed ; it is very slightly hooked. Adductor ridge 

 not quite confluent with the articular ridge, bounding the cavity for the depressor muscle ; 

 it is rather prominent, as Darwin says it generally is in var. coccopoma and var. concinnus. 

 The cavity for the lateral depressor muscle is deep, as, according to Darwin, is only 

 the case in the two varieties just mentioned, and sometimes in var. communis. The 

 surface of the valve is slightly externally depressed in the line of the adductor ridge. 



The tergum is broad, the longitudinal furrow is closed. Apex only indistinctly 



