part 8] THKOUGH THE ANDES OF PEEU A^T> BOLIYIA. 253 



members of the same group found in the Oomia Beds of Cutch 

 and in the Uitenhage Beds of South Africa (now generally 

 regarded as Neocomian).^ This is shown by the possession of two 

 series of obliquely-inclined ribs which meet along a line joining 

 the umbo of the shell with a point on its ventral margin, to form 

 an angular or V-scrijyta type of ornament. Since the material at 

 my disposal is not sufficiently good to indicate the early stages 

 of growth, it is impossible to say whether this is a homogenetic 

 character shared alike by the South American, Indian, and South 

 African forms, or whether it has been attained by convergence of 

 heterogenetic lines of development. 



Such being the case, in the absence of associated forms common 

 to the three sets of deposits, it would be unsafe to regard these 

 shells as furnishing conclusive proof of contemporaneity. If 

 taken in conjunction with the presence of Acantlwdiscus, 

 however, the peculiar nature of their ornament is not without 

 significance. 



Palseontological Note. 



Tbigonia lorentii Dana. (PI. XV, fig. 7.) 



In order to illustrate the structural differences whicli exist between this 

 and the closely- allied forms from South Africa and India the following- note 

 may be added to the description of the species given by Prof. C. I. Lisson 

 C Geologia de Lima, &c.' 1907, p. 32 & pL iii, figs. 2-3). 



From Trigonia vau Sharpe (F. L. Kitchin, Ann. S. Afr. Mus. vol. vii, 1913, 

 p. 110 & pi. vi, figs. 1-3, ' Invertebrate Fauna & Palaeontological Relations 

 of the Uitenhage Series ') T, loyentii is distinguished by its triangular shape 

 and absence of posterior elongation. In the former species the number of 

 ribs in the anterior and the posterior series is approximately equal, whereas 

 in the Peruvian form those in the anterior series are twice as numerous. 

 In T. lorentii, moreover, the ribs are strongly and completely developed in 

 the adult shell, while in Sharpe' s species the anterior series tend to die out 

 near the frontal margin before the individual has attained more than half 

 its growth. 



From Trigonia stotvi Kitchin {ibid. p. 115 & pi. vi, figs. 4-5, pi. vii, fig. 1) 

 it differs in the possession of a rounded anterior margin as opposed to the 

 angular shape of that species, in the regularity and greater obliquity of the 

 V"s, and in the absence of a siphonal gape. 



From Trigonia duhia Kitchin (' Palseontologia Indica ' ser. ix, vol. iii, pt. 2, 

 1903, p. 67 & pi. vii, figs. 3-5) it differs in general outline and degree of in- 

 flation (this being considerably less in the Peruvian form), while the ribs are 

 narrower and more angular. 



From Trigonia V-scripta Kitchin {ibid. p. 70 & pi. vii, figs. 6-8, pi. viii, 

 figs. 1-3) it is easily distinguished by the regularity of its ribbing and the 

 obliquity of the Vs. 



Individual shells in my collection are seen to vary considerably in the 

 details of their ribbing ; but, without examining a large number of specimens, 

 it is impossible to say whether they are of sufficient importance to rank as 

 separate species. 



1 W. M. Gabb, in describing a collection of fossils made by Dr. Antonio 

 Raimondi in Peru, says, in speaking of Trigonia lorentii, 'from its type, 

 evidently Jurassic ' ; and Raimondi himself was of the opinion that the beds 

 of Salto del Fraile were of Liassic age. Journ. Acad. Nat. Sci. Philad. 

 ser. 2, vol. viii (1874-81) pp. 288-89. 



