The Invertebrate Fauna of the Uitenliagc Series. 71 



GENUS LIMA J. G. Bruguiere. 



SUB-GENUS ACESTA H. and A. Adams. 



LIMA (ACESTA) OBLIQUISSIMA Tate. 



Plate II., fig. 7. 



1867. Lima obliquissima E. Tate, Quart. Journ. Geol. Soc., vol. xxiii., 

 p. 156, pi. ix., fig. 5. 



Supplementary Descriptive Note. The shell has great height in 

 comparison with length. The posterior outline is gently rounded, 

 the anterior profile straight. The straight anterior border passes 

 at its lower end by a somewhat sudden curve into the rounded 

 inferior border. The valves are most convex in the umbonal half and 

 near the anterior side ; they become flatter posteriorly and inferiorly. 

 Anteriorly, the flank passes abruptly, though without marked cari- 

 nation, into an extensive, flat frontal face, truncating the shell. This 

 frontal area is in no degree sunk or concave in form. The umbones 

 are acute and sharp, terminal at the anterior extremity of the 

 hinge-line; the superior border of the shell is straight and very 

 short, and truncates the shell to form a right angle with the 

 anterior border. The anterior ear is rudimentary or not developed ; 

 the posterior ear is much reduced, and not definitely demarcated 

 from the flank. 



The ornamentation consists of delicate linear radial grooves, 

 very crowded near the umbo, gradually diverging until, at a distance 

 of 40 rnm. from the umbo, they may be separated by interspaces 

 2 mm. broad. At a distance exceeding 30 mm. from the umbo, these 

 lines are almost or quite absent from the middle part of the flank, 

 though well impressed on the lateral parts. The lines follow a 

 more or less irregular and wavy course and are sometimes suddenly 

 deflected to right or left when traced down from a prominent 

 concentric growth-line. When well preserved, the linear orna- 

 ments show a minutely punctate structure, most perfectly developed 

 in the umbonal half of an adult shell. The interspaces are very 

 gently convex or are flat, but are without sculpture. On the frontal 

 area the ornaments are of a more pronounced character, and may 

 take the form of imbricating ridges with the edges directed away 

 from the valve-margin. They radiate from the umbonal region 

 and pass along the frontal face, gradually approaching the frontal 

 valve-margin and forming an acute angle with this. On the frontal 

 area, therefore, the ornaments are very obliquely crossed by the 

 lines of accretion. 



