ORTMANN : TERTIARY INVERTEBRATES. 251 



scutal angle; the basal margin, on each side close to the spur, curves 

 toward it ; articular ridge of inner side very prominent. 



Diameter of largest conical individual at base, 30 mm ; height of largest 

 elongate individual, 43 mm. 



Remarks: Among the many Balani from the Patagonian beds at 

 hand, the external form is very variable, but there may be distinguished 

 three chief forms: (i) short, conical, with distinct folds on the parietes ; 

 (2) short, conical, with smooth parietes ; (3) elongate, with smooth parie- 

 tes. There are, however, intermediate forms. The first two forms gene- 

 rally grow isolated, the last crowded in colonies. I possess a large 

 colony that shows a number of elongated individuals of form 3, but the 

 marginal ones are shorter, and represent form i. This disposes of Phil- 

 ippi's opinion, that the folded form (fig. 6, of Sowerby) is different. More- 

 over, all the folded individuals are true Balani, and do not belong in the 

 genus Chthamalus, as Philippi believes, since the rostrum possesses radii, 

 not alae, as is the case in Ckthamalus. 



In most of my specimens the parietes are imperforate, as Darwin 

 states, but sometimes pores are visible : these pores are most distinctly 

 seen in a small colony from 30 miles north of Rio Chalia. 



Darwin describes the scutum, and describes and figures the tergum. I 

 possess one scutum and 2 terga taken from the interior of a specimen of 

 form 3, and 7 scuta and i (broken) tergum obtained by washing the ma- 

 trix from the exterior and interior of the colonies (all from San Julian, 

 Oven Point). Upon a lower valve of Ostrea ingens from the same local- 

 ity there are 21 individuals of the varieties i and 2, of which no less than 

 5 show the opercular valves in situ : most of them are firmly imbedded, 

 but in one individual of van i, I have extracted one scutum and tergum. 

 Both agree with those taken from var. 3, although the spur of the tergum 

 is broken off. 



The most prominent features of the opercular valves are, that in both, 

 scutum and tergum, the articular ridge is very prominent, that the scutum 

 is comparatively narrow, and has no radial sculpture, and that the spur of 

 the tergum is narrow and short. In these characters, R. various strikingly 

 differs from the externally similar species of the Cape Fairweather beds. 



Whether the specimens recorded by Philippi (p. 225) under the name 

 of Chthamalus antiquits from Punta Arenas (from Ostrea torresi, and ac- 

 cordingly from the Magellanian beds) really belong to this species re- 



