PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
170 
Gen. GIBBULA Riss. 
102. Gibbula laevis (Sowerby). 
PI. XXXI, Fig. 8. 
1846 Trochus Icevis Sowerby, in: Darwin, Geol. Observ. S. Amer., p. 256, 
pi. 3, f. 46, 47 (adult). 
1846 T. collaris Sowerby, ibid., p. 256, pi. 3, f. 44, 45 (junior). 
1887 ^ tevis Philippi, Tert. & Quart. Verst. Chiles, p. 101, pi. 12, f. 5. 
1897 Gibbula coll. v. Ihering, in: Rev. Mus. Paul., v. 2, p. 273. 
1899 G. c. v. Ihering, in: N. Jahrb. Miner., etc., v. 2, p. 24. 
Shell conical, broader than high, umbilicated. Surface smooth, whorls 
almost flat, only the last one slightly convex. Periphery sharply angu- 
lated. Upper whorls, close to the suture, with a series of small tubercles. 
Base very slightly convex, with a deep umbilicus of medium size, and a 
number of fine revolving striae, which are distinct near the umbilicus, but 
disappear toward the periphery. 
Height (not complete), 28 mm; diameter, 51 mm; according to Phil- 
ippi : height, 38 mm ; diameter, 50 mm. 
Remarks : Philippi was the first to recognize that T. collaris of Sowerby 
is only the young stage of T. Icevis , and he retains the specific name of 
the old stage. V. Ihering again uses the specific name of collaris , preced- 
ing that of Icevis in Sowerby’s text, but according to the rules of nomen- 
clature, we are to follow Philippi, who was the first to make a selection 
between the two names available. 
In some specimens the small tubercles near the suture disappear later 
than in others. The lower surface of the shell has spiral striae, which in 
very young ones are very faint near the periphery, and disappear in old 
shells altogether, with the exception of 5 to 7 close to the umbilicus (see : 
Sowerby’s figure 47). 
Record of specimens : Mouth of Santa Cruz River, 12 sp. ; Las Salinas, 
1 sp.; San Julian, Oven- Point, 2 casts; Lake Pueyrredon, base of Ter- 
tiary, 2 casts ; Lake Pueyrredon, 6oo r above base, 1 cast. 
Distribution : Patagonian beds of Santa Cruz (Sow., v. Ih.); Navidad 
(Sow., Phil.), Lebu (Phil.). 
Affinities: A very closely allied species is T. venefims Philippi (1887, 
p. 1 01, pi. 12, f. 8), from Navidad, but the latter has a blunt, but distinct 
angulation near the suture, on which the tubercles are placed. 
