122 PATAGONIAN EXPEDITIONS : PALEONTOLOGY. 



into the posterior margin. Ventral margin slightly concave. Apex situ- 

 ated a very short distance from the anterior end. 



Remarks: Our specimens differ from the original description in the 

 more ventricose valves and apex, but the general form agrees well with 

 v. Ihering's species, so that I do not think they are different. 



Record of specimens : Mouth of Santa Cruz River, i right valve ; Mt. 

 of Observation, upper horizon, i left valve. 



Distribution : Jegua quemada, Suprapatagonian beds (v. Ih.). 



Affinities: Our specimens come very near to M. coquimbana of Philippi 

 (1887, p. 203), especially to the variety figured in Philippi's pi. 44, f. 7, 

 from the Pliocene of Coquimbo, Chili. In M. coqiiimbana, however, the 

 apex is more anterior. 



45. MODIOLA ANDINA Ortmann. 



PL XXIV, Fig. 4. 

 1900 M. and. Ortmann, in: Amer. Journ. Sci., v. 10, p. 370. 



Shell small, elongate, about 2^ times as long as high. Apex near 

 anterior end. Both valves convex, with a blunt ridge running down from 

 the apex to the posterior and inferior end. This ridge is curved, the con- 

 cave side of the curve directed toward the lower margin. Upper margin 

 almost straight in its anterior (cardinal) part, forming a blunt angle with 

 the posterior part, which is almost straight, and passes by a regular curve 

 into the rounded posterior margin of the shell. Ventral margin distinctly 

 concave, and forming with the posterior margin a right, but blunt angle. 

 Surface of shell finely radially striated in the upper part, i. e., above the 

 oblique ridge crossing the valve ; the striae most distinct near the poste- 

 rior half of upper and near posterior margin. Lower part of shell, below 

 the ridge, smooth, only with few lines of growth. Anterior end of shell, 

 below and in front of the apex, with a few (5-7) fine striae, which are often 

 very indistinct. 



Measurements: Length, 24, 23 mm. 

 Height, 9, 10.5 mm. 



Remarks: No Modiolce are known from South American deposits that 

 might be compared with this one. In M. rugulosa and keviuscula of 

 Philippi (both from Lebu, Chili), radial striae are present, but they are not 

 distributed in the particular manner as in this species, and, furthermore, 

 the outline of the shell is quite different. 



