Argopecten cristobalensis (Hertlein, 1925)
HERTLEIN, L. G. 1925. Pectens from the Tertiary of Lower California. Proceedings of the California Academy of Sciences [4th Series], 14 (1): 1-35, pls. 1-6. [p. 19, pl. 3, figs. 1, 2, 5]
1925 Pecten (Plagiotecnium) cristobalensis Hertlein, 1925
L. G. Hertlein, 1925, plate 3
|
«Shell large, fairly thick, in several specimens with strong lines of restricted growth; valves moderately arched. Right valve ornamented by about 24 flat-topped, squarish, radiating ribs, separated by flat-bottomed, slightly narrower, interspaces, the whole surface crossed by well defined, wavy, concentric lines of growth ; anterior and posterior margins of valve smooth except for concentric incremental sculpture; ventral margin evenly rounded; ears unequal, the anterior ear with a large byssal notch, and ornamented by about five radiating riblets crossed by concentric lines of growth; the posterior ear also bearing about five or six radiating riblets crossed by growth lines. Left valve slightly more convex than right and sculptured much as the latter, the anterior and posterior margins with concentric lines of growth only; ears ornamented by about eight or nine radiating riblets, the anterior ear with a slight notch. Altitude 117 mm.; longitude 135 mm.; diameter right valve approximately 17 mm.; apical angle of right valve approximately 100° - 110°.
Type: Right valve. No. 36 (L.S.J.U. type collection), from Loc. 49 (L.S.J.U.), slopes of Salada three miles southeast of Turtle Bay, uppermost beds, San Cristobal Bay Quadrangle, Lower California; Paratypes: No. 27 (L.S.J.U. collection) and Nos. 1775, 1776 (C.A.S. collection), B. F. Hake collector; Salada, Pliocene. The species was also found at Loc. 48 (L.S.J.U.), at the mouth of a large arroyo northwest of Elephant Mesa, Scammon Lagoon Quadrangle, Lower California. Pecten cristobalensis is distinguished from P. cerrosensis mendenhalli Arnold, by its squarish, more numerous ribs. The greater number of radial, squarish ribs, separated by narrower interspaces, and the less strong development of concentric incremental lines, distinguish the present species from P. cerrosensis Gabb proper. P. cristobalensis has a large byssal notch in the anterior ear of the right valve, and the ears are more strongly sculptured by radiating riblets than in P. cerrosensis, in which the byssal notch is very slight, and, except for lines of growth, the ears are smooth. From P. callidus Hertlein, P. cristobalensis differs in the more numerous ribs, different ears, and rounder outline. The distinction between the present species and P. purpuratus Lamarck is based largely upon the character of the radial ribs and of the anterior ear of the right valve. The ribs of P. purpuratus are wider and lower than those of P. cristobalensis; and conversely, the interspaces are narrower in P. purpuratus; furthermore the ribs of the latter species expand much more rapidly toward the ventral margin than do those of P. cristobalensis. The lateral serrations on the radial ribs, so strongly developed in Lamarck's species, are very slight in the present form. The presence of three very strong ribs on anterior ear of right valve of P. purpuratus with only a vestige of a fourth, rather than five less strong riblets as in P. cristobalensis, is also an evident and apparently constant difference». LEO GEORGE HERTLEIN, 1925
|