Ortmann — Invertebrate Fossils from Patagonia. 371 



10. Nucula reticularis sp. nov. Shell small, moderately 

 convex and moderately thick, subovate, oblique. Posterior 

 and anterior dorsal margin slightly convex, ventral margin 

 strongly arcuate. Surface with very fine concentric ribs, which 

 are irregular and often bifurcate. These ribs are crossed by 

 still finer radial strise, which give a beautifully reticulated 

 appearance to the shell. Ventral margin finely crenulated on 

 inner side. Hinge teeth fine, both parts of the series forming 

 an obtuse angle, anterior part with ca. 9, posterior with ca. 18 

 teeth. Length, 7'5 mm ; height, 6 mm . 



The sculpture of this species is of the type of that of the 

 Oligocene N. chasteli JNyst. 



Santa Cruz and Mt. of Observation. 



11. Crassatella quarta sp. nov. Shell elongated-ovate, 

 comparatively thin, not very convex. Apex only slightly 

 prominent. Anterior end rounded, posterior hardly angulated 

 and hardly narrowed. Posterior dorsal margin straight near 

 apex, anterior almost straight, with only a slight suggestion of 

 concavity close to the apex. Surface ornaments as in C. Lyelli 

 Sowerby, but the ridges more crowded and a little less devel- 

 oped. Ventral margins without crenulations. Length, l7 mm ; 

 height, 10 mm , but growing larger. 



Santa Cruz ; Lake Pueyrredon. 



12. Glycimeris regularis sp. nov. Shell elongate, convex, 

 with concentric lines of growth and undulations. Apex at \ 

 of the length, incurved. Anterior end rounded, posterior 

 subtruncated, not narrower than anterior. Ventral margin 

 straight in the middle. Long., 78 ; height, 45. 



This form does not agree with any of the described Pata- 

 gonian species, and accordingly I think it is new, although all 

 the distinctive characters are taken only from the external 

 form. 



Santa Cruz; San Julian; Lake Pueyrredon. 



18. Corbula hatcheri sp. nov. Shell small, solid and thick, 

 subovate- triangular. Right valve very little larger than the 

 left, both moderately convex. Anterior end rounded, pos- 

 terior produced, subtruncated, an angular ridge running from 

 apex to posterior angle. Ventral margin arcuate, posteriorly a 

 little concave. Lower margin of right valve reflected toward 

 the left valve. Surface with concentric ribs, which are rounded 

 and rather crowded. Length, 11 ; height, 7'5 ; diameter (of 

 right valve), 2'5 mm . ^ 



Santa Cruz ; Las Salinas ; Mt. of Observation ; San Julian. 



14. Martesia pumila sp. nov. This species resembles much 

 M. patagonica Phil, but is much smaller, the callous plate of 

 the anterior margin is very small, and the ribs of the anterior 

 part of the shell form a very obtuse angle with the lines of 



