248 
PATAGONIAN EXPEDITIONS ! PALAEONTOLOGY. 
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, 1 carina. 
Affinities : The affinities to the upper Cretaceous S. solidulum have been 
explained above. 
Fam. V ERR U Cl DAC Darw. 
Gen. VERRUCA Schum. 
175. Verruca laevigata Sowerby. 
PL XXXVIII, Fig. i“- c . 
1854 V. /. Darwin, Mon. Cirrip. Balan., p. 520, pi. 21, f. 3. 
1900 V. /. Ortmann, in: Amer. 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. Icevigata. 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 V. stroemia ), and 
the upper articular ridge short. The movable tergum ( T) is broad. In 
our figure i 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 i 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 b 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. 
