Appendix to Part II 623 



the species belongs to that section of the genus which has 

 acuminated and soJid parietal valves. But the most variable part, 

 in form, is the basal valve. It is to be observed that in most, if 

 not in all, the species of this genus which have been brought from 

 the Southern Hemisphere, it is the base that becomes tubular 

 whenever any accidental circumstance causes the shell to be 

 elongated ; whereas in the elongated and clavate varieties of our 

 common species, it is the parietal valves that are lengthened and 

 not the basal. Thus, with respect to the present species, we find 

 that when any number of individuals are placed close together 

 when very young, as they increase they form a group, of which 

 the basal valves grow up side by side and become tubular, without 

 the parietal valves changing in form ; hence in some specimens 

 this valve is concave inconsequence of its having been placed upon 

 a convex substance, and at a distance from each other ; while, in 

 others, which have been placed very closely together when very 

 young, this basal valve has taken a more or less deep cup shape, 

 being very small at its lower extremity and increasing in dimen- 

 sions with age 



San Julian, Patagonia. 



Balantjs Coqtjimbensis. — PI. II. fig. 7. 



Balanus testa polymorphd, valvis Icevibus, nonnunquam radiatim 

 striatis, later alibus posticis angustiwibus ; apicibus subtruncatis ; 

 aperturd parvuld. 



A remarkable fact is* observable in the specimens, both from 

 the upper and lower parts of the formation ; I have selected one 

 from the upper bed as showing it most distinctly. In consequence 

 of numerous individuals being closely grouped together, each one 

 has been compelled to lengthen the basal valve, so as to form a 

 nearly cylindrical tube, closed at the lower part, and gradually 

 increasing as it ascends until it joins the base of the six parietal 

 valves: this increase in the length of the base seems to have 

 taken place more rapidly than the growth of the animal would 

 permit. A portion of the lower part of this basal tube has, there- 

 fore, been filled up with cells or vesicles separated by calcareous 

 septa, very irregular indeed, but which would, nevertheless, 

 answer the purpose of supporting the base of the animal in 

 the tube, so as to enable the animal to continue its vital 

 functions. 



Coquimbo, Chile. 



