140 STUDIES IN GEOLOGY, No. 3 



material in the Nelson collection. It is apparently, not closely 

 similar to any known American species. Dosinia orbicularis 

 -Agassiz, 156 of the Miocene of Italy, France, and Austria, 

 agrees in every character save that the beaks are far more 

 anterior. 



Variegated. South of Quebrada Boca Pan. 



Dosinia (Dosinidia) delicatissima Brown and Pilsbry 



Dosinia (Artemis) cf acetabulum Conr. Toula, Jahrb. k.k. geol. 

 Reichs., Bd. 58, p. 727, p. 27, figs. 8, 8a, 1908. 



Dosinia delicatissima Brown and Pilsbry, Proc. Acad. Nat. Sc. 

 Phila., vol. 64, p. 516, pi. 26, fig. i, 1912. 



Shell of moderate size, lentiform, slightly inflated, thin 

 and very delicate. Entire margin subcircular in outline. 

 Umbones not prominent, inclined slightly forward, pointed. 

 Surface convex, lentiform. Sculpture of many concentrically 

 arranged flat ribs, with very narrow interspaces which are 

 finely and delicately graven on the flat surface. Lunule 

 heart-shaped, deeply impressed, striated by fine lines which 

 are the continuation of the concentric sculpture. Escutcheon 

 absent or very slightly marked. Hinge moderately strong, 

 normal. Muscle scars and pallial.line feeble. Dimensions 

 of two specimens: Length, 51.5; height, 49.5; (semi) diam- 

 eter, 12 mm. Length, 65; height, 62; diameter, 31 mm. 



This delicate and beautifully sculptured shell is common 

 in the Lower Zorritos. The thickness of the Peruvian shells 

 varies somewhat, some being proportionally even thinner 

 than those cited by Brown and Pilsbry from Gatun, but the 

 chief characters agree perfectly. 



Toula's figured specimen agrees entirely with the speci- 

 mens from Peru, with the possible exception that his form 

 does not appear to have so deeply impressed a lunule ; how- 

 ever, faulty reproduction in his figure might account for that. 



^Hoernes, M., Abh. k.k. geol. Reichs. Bd. 4, p. 142, pi. 16, fig. I, 

 1862; Sacco, Piemonte, parte 28, p. 48, pi. 11, fig. 10, 1900. 



