Euvola illesca (Olsson, 1932)
OLSSON, A. A. 1932. Contributions to the tertiary Paleontology of Northern Peru: part 5. The Peruvian Miocene. Bulletins of American Paleontology, 19 (68): 1-272, pls. 1-24. [p. 80, pl. 4, figs. 4, 6, 7, 12; pl. 5, fig. 7]
1932 Pecten (Pecten) illesca Olsson, 1932
A. A. Olsson, 1932, plates 4, 5.
|
«Shell small, inequivalve, strongly sculptured; the right valve is strongly convex, its greatest inflation being in the center while the left valve is flattened, somewhat arched in the lower or ventral portion; in the right valve, the sculpture consists of high, square ribs which number about 18, the largest in the middle and smaller towards the sides; the interspaces are deep, of the same width as the ribs; in the left valve, the ribs number about 17 and are narrower, somewhat lower with wider interspaces; both valves show a fine, secondary sculpture which is best developed on the left valve; in the left valve, this consists of a fine ridge or thread on the sides of each rib and a peculiarly frimbriated cross-threading in the interspaces; this submiscroscopic sculpturing is much finer on the ventral part of the valves; in the right valve, the ribs are not bordered by the secondary rib or thread but the submicroscopic sculpture seems the same; ears very small, especially in the right valve; hinge crura strong.
Length, 19.25 mm.; height, 19 mm.; semidiameter, 7 mm.; (right valve. Length, 19 mm.; height, 18 mm.; semidiameter, 2 mm. (left valve). Remarks.— This small species is locally very common in the Sechura Miocene. It appears to be a true Pecten, the right valve being very convex while the left valve is nearly flat or simply arched in the ventral region during its mature or gerontic stages. The ears are extremely small in the right valve, somewhat larger and subequal in the left. In addition to the strong ribs there is a delicate, submicroscopic sculpture best seen in the interspaces of the left valve. In the Sechura collection, there is an imperfect left valve and numerous fragments of a species akin to Pecten gatunensis Toula, from Panama. The ribs seem to widen out more rapidly on the Peruvian shell but the material is too fragmentary for close comparison. Locality and Geologic Occurrence.— Montera formation. Zone A, Que. Montera.» AXEL ADOLPH OLSSON, 1932
|