76 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



1873 Wahlhcimia p. Hutton, Cat. Tert. Moll. Ech. New Zealand, p. 36. 



1885 W. p. Hutton, in: Quart. Journ. Geol. Soc., v. 41, p. 553. 



1887 Tercbratula p. Philippi, Tert. Quart. Verst. Chil., p. 217, pi. 49, f. 



2 (after Sovverby). 



1897 Magcllania p. v. Ihering, in: Rev. Mus. Paul, v. 2, p. 267. 

 1899 Tcrcbratella p. Lahille, in: Rev. Mus. La Plata, v. 9, p. 289, ff., 

 pi. i, 2. 



Shell oval, more or less elongate, rarely almost as broad as long. 

 Both valves nearly equally convex. Beak incurved, with a large foramen ; 

 beak ridges blunt. No sinus on the dorsal (smaller) valve. Surface 

 smooth, without ribs. 



Measurements: Length, 59, 40, 30, 25, 34, 31, 27 mm. 

 Width, 51, 32, 28, 19, 25, 21, 25 mm. 



Remarks: This species is a Tcrcbratella as has been shown by Lahille, 

 who figures the complete brachial apparatus (pi. i, f. 53, 54, 55). Al- 

 though I do not possess any specimens showing this apparatus complete, 

 the median septum of many of my specimens shows distinctly a cruciform 

 appearance, /. <?., it possesses, near the lower end, processes, which appar- 

 ently were connected with the descending part of the loop. The latter, in 

 numerous individuals, shows an angular projection just where we are to 

 expect this connection, so that there is every reason to believe that a 

 bridge extended between the descending branch of the loop and the 

 median septum. And further, the close affinity of T. patagotiica with the 

 following species ( T. gigantea) from which it is hardly distinguishable 

 specifically supports this view, the latter being a true Terebratella. 



Lahille has written a separate paper on the variability of this species. 

 Although we must appreciate the value of such studies, they never can be 

 satisfactory, if the author does not pay due attention to the stratigraphical 

 position of the forms in question. I am very much afraid that Lahille in 

 his paper confused the present form and the next one; at any rate, I 

 doubt very seriously that his statement, that T. patagonica is found asso- 

 ciated (p. 5 of separate copy; "dans la meme couche") with Mouopliora 

 darivini, is correct. The latter species, according to v. Ihering (1899, p. 

 42), belongs to the Entrerios formation, which is younger than the Pata- 

 gonian, and I am fully prepared to accept this opinion, since among our 

 collections from Patagonian beds not a single individual of Monophora is 

 found, while T. patagonica is very abundantly represented. If Lahille 



