Clark: The San Lorenzo Scries of Middle California 173 



Family Nyctilochidae 

 Genus BURSA Bolten 

 BUKSA MATHEWSONII (Gabb) 

 Plate 20, figures 1 and 2 

 Banella maihewsonii Gabb, Geol. Surv. Calif., Palaeontology, vol. 2, p. 8, 

 pi. 2, fig. 13, 1868. 



Banella mathewsonii Gabb, Smith, Proe. Calif. Acad. Sei., ser. 4, vol. 3, 



pp. 176, 179, 1912. 

 Bursa mathewsonii (Gabb), Clark, Univ. Calif. Publ., Bull. Dept. Geol., 

 vol. 9, no. 2, p. 15, 1915. 



Shell heavy, robust, medium in size to fairly large ; spire high ; tops of all 

 specimens examined broken but probably with not more than seven, possibly eight, 

 whorls; sutures depressed. Surface sculptured by about fourteen or fifteen longi- 

 tudinal, rather coarse, rounded ribs, which are nodose, due to the fact that they 

 are crossed by spiral ribbing which, on the smaller specimens, is not quite so 

 heavy as the longitudinal ribbing, but on the larger specimens this spiral ribbing 

 may become the more prominent. Interspaces between the spiral ribbing slightly 

 wider than the tops of the ribs, and in each interspace there is a narrow, spiral 

 riblet. On the whorls of the spire there are four of these major spiral ribs; on 

 the body whorl there are nine or ten. On the surface of the shell there are two 

 fairly strong, continuous, rope-like varices, one of which is usually close to the 

 outer lip, the other on the opposite side of the whorl. Mouth ovate in outline- 

 inner lip incrusted; canal short and rather abruptly recurved. 



Dimensions. — Pleseotyjie: height, about 15 mm.; height of body whorl, about 

 10 mm. ; maximum width of body whorl, about 10 mm. 



Occurrence. — University of California localities 1131 and 2754. 



Family Columbellidae 

 Genus COLUMBELLA Lamarck 

 COLUMBELLA (MITKELLA) TENUILINEATA, n. sp. 

 Plate 22, figures 2 and 3 

 Type specimen 11221, Coll. Invert. Palae. Univ. Calif., loc. 1131 

 Shell small, fusiform ; spire fairly high ; apex acute. Number of whorls six 

 or seven ; body whorl higher than wide, about half the height of the shell ; sutures 

 marked by a depressed line. Sides of whorls gently convex ; base of body whorl 

 rounded, the whorl narrowing rapidly toward the anterior end of the canal. Sur- 

 face of shell sculptured by medium fine, spiral ribs, with interspaces which appear 

 as narrow, incised lines ; on the body whorl are about eighteen, and on the whorls 

 of the spire six or seven of the spiral ribs, which tend to be nodose due to the 

 fact that they are crossed by fine longitudinal ribbing. As counted on the body 

 whorl there are at least thirty of the fine longitudinal ribs, the interspaces between 

 which are approximately equal to the width of the ribs. The longitudinal ribbing 

 tends to become obsolete on the body whorl and, on some specimens, even on the 

 lower whorls of the spire. Aperture narrow, elongate-subovate ; outer lip thin, 

 denticulate internally; inner lip not incrusted. Canal short, narrow and straight. 



Dimensions. — Height, 4 mm. ; height of body whorl, 2.25 mm. ; greatest width 

 of body whorl, 2 mm. 



Occurrence. — University of California locality 1131. 



