| Home> Miocene>

List species

Lithatractus timmsi Campbell and Clark, 1944

Description - Add description

Shell rather large, ovoidal, with two prominent, opposite, equal polar spines, wich are long (1.23 times long as axis of shell), strongly conical (5°), minutely blunted and irregular at tip as if subjected to pressure and compressed (perhaps points of attachment of protoplasmic strands), and swordlike, with four similar, triangular blades with sharp edges and with bases merged seperately on surface of cortical shell, blades at equal angels from each other in two crossed pairs (in our specimen one polar spine was broken off near base, but it is asumed to be duplicate of other); cortical shellgenerally egg-shaped, its longer axis (vertical axis, in line with polar spines) 1.13 times diameter of minor (transverse) axis, and with sides evenly contured; medullary shell ralatively large (its long axis 0.54 long axis of cortical shell), its transverse axis 0.85 diameter of lng axis, and its sides regulary contoured to poles; radial supports (10?), two very strong, prismatic polar, four thinner radials, and four thin transverse, save polar ones, rodlike; pores of cortical shell subuniformly elliptical, only a few odd ones larger and of different form, shallow, narrowly double contoured, well spaced,and about 18 in long axis and 15 in transverse axis, of medullary shell about 10 in long axis and eight or nine in transverse axis, larger and more nearly squarish or subcircular than in cortical shell, deeper set and more widely seperated; wall of cortical shell thicker than of medullary shell; surface of cortical shell slightly roughened with short points. Length, total (estimated on assumption that both polar spines are equal), 282µ, of polar spine, 99µ; diameter of pores of cortical shell, 4.4-6.6µ.
Lithatractus timmsi n. sp. differs from pachystylus (Haeckel, 1887) in lack of funnelshaped pores. In addition, it has much longer polar spines than latter, wich is only other one of subgenus Lithatractara with tetrangular polar spines.
Campbell and Clark 1944











Discussion / Comments


Web links