﻿70 PKOCEEDINGS OP THE GEOLOGICAL SOCIETY. [Nov. 21, 



Pig. 20 represents a young specimen. The outline is much more 

 rounded, however, if that be not due to pressure ; and the duplicated 

 striae cover all the surface. 



Locality. West slope of Illampu. [Fielclmarshal Brown, a well- 

 known general of the War of Independence, and after whom this 

 shell is named, showed much interest in these researches, and was of 

 great assistance to the author of the foregoing memoir. — D. F.] 



Bellerophon, sp. 



About 1 inch wide, having a large body- whorl, a small spire, and 

 the whorls not at all involute ; umbilicus quite open, and the 

 whorls sloping towards it. Striae of growth arched backwards to 

 the carinate margin, which, however, is obtuse, not sharp-edged. 



Locality. Common enough in some hand-specimens from the west 

 side of Illampu. 



Patella or Pileopsis ? 



An extraordinary specimen of a subovate clypeiform shell, an inch 

 and. a half in its largest diameter, and rather more than an inch 

 wide, has an excentrie blunt umbo, and a rather wavy margin. The 

 surface is covered with close concentric ridges, which show equally 

 well on the external and internal cast. The general appearance is 

 that of an oblique Patella, or rather one of the Calyptrceiclce. But it 

 is too imperfect to decide upon. Patelliform shells are known in the 

 Silurian, but they are very rare. 



Locality. West side of the Valley of Millepaya. 



LOWEE ? SILURIAN. 

 Cbttziana, D'Orbigny. 



It seems hardly worth while to separate these obscure fossils into 

 several genera while we know so little of them; but certainly 

 they cannot all belong to one group. The distinctly grooved and 

 bilobed form, which induced M. Cordier to apply the name Bilobites 

 to them, is characteristic of the species described by D'Orbigny, 

 and of some others found in N. America. The more elongate strap- 

 shaped species found in Europe have already received names from 

 M. Rouault in his memoirs on the Silurian Rocks of France. And 

 the species here figured belong to such various plans of form that, 

 if we only knew a little of the nature of the bodies in question, we 

 should be bound to give them separate names; at present I only 

 propose one for the sagittate forms — Boliviana. Mr. Forbes did 

 not meet with either of D'Orbigny's species, which, from that au- 

 thor's description, came from Lower Silurian beds*. Those here 

 described are also the lowest fossils in the section. 



* " C'est le premier corps organist qui se montre au-dessus des phyllades 

 schistoides, dans les phyllades inicaces brunatres." — Voyage, &c. vol. iii. part 4 

 (Paleontologie), p. 31. Mr. Forbes thinks, however, that there is no evidence of 

 then' being so low in the series. 



