248 PATAGONIAN EXPEDITIONS I PALEONTOLOGY. 



radial ribs on the tectum, and the distinct separation of the .parietes from 

 the tectum by a blunt ridge. 



Record of specimens : San Julian, Darwin Station, i carina. 



Affinities : The affinities to the Tipper Cretaceous S. soliduhim have been 

 explained above. 



Fam. VERRUCID^. Darw. 



Gen. VERRUCA Schum. 

 175. VERRUCA LEVIGATA Sowerby. 



PL XXXVIII, Fig. I"". 



1854 V. 1. Darwin, Mon. Cirrip. Balan., p. 520, pi. 21, f. 3. 

 1900 V. I. Ortmann, in: Arner. Journ. Sci., v. 10, p. 379. 



Walls of the shell smooth. Movable scutum with the lower articular 

 ridge broader than the short upper articular ridge; movable tergum 

 broader than high, with the upper articular ridge produced into a point. 



Diameter of largest individual, 5.5 mm. 



Remarks: I cannot find any difference between our fossil form and the 

 living V. l&vigata. The walls of the shell are smooth, with concentric 

 lines of growth, without radiating ribs. The movable scutum has the 

 lower articular ridge broad (decidedly broader than in y. strcemia), and 

 the upper articular ridge short. The movable tergum ( T] is broad. In 

 our figure \ c on plate XXXVIII, the scutum appears to be narrower than 

 in fig. 3 of Darwin, but one must bear in mind, that our figure represents 

 only the exposed parts of scutum and tergum ; of the occludent margin 

 (the convex one) a part is covered by the occludent margin of the fixed 

 scutum, and is not shown. The same is the case with the basi-carinal 

 angle of the tergum. 



Of the three complete specimens, two have the left hand scutum and 

 tergum fixed, and the third is reversed, i. e., with the right hand scutum 

 and tergum fixed (compare Darwin's figure i a and \ d on pi. 21). Darwin 

 says that the latter case (left opercular valves movable) appears to be 

 more common in the recent form. 



The reversed specimen is the largest. The figure i* was drawn from a 

 combination of the two others, each 4 mm in diameter. The fourth in- 

 dividual, with the movable opercular valves missing, is still smaller. 



