LIMA. 23 



regular curve. Umbones small, close together. Apical angle usually about 100, 

 but sometimes only 90. Ears small, the posterior larger than the anterior. 

 Anterior area of moderate size, very deep, with a sharp edge and numerous radial 

 ribs. 



Ornamentation consists of numerous, well-defined, radial grooves with distinct 

 pits, covering the entire surface of the shell. The grooves are straight or slightly 

 wavy, and in some cases are linear, in others broader, the latter giving the appear- 

 ance of flattened or rounded ribs to the interspaces. The pits in the grooves some- 

 times extend into the sides of the ribs. New grooves may be introduced near the 

 ventral margin or occasionally near the middle of the valve. In well-preserved 

 specimens very fine concentric ridges are sometimes seen. A few growth-rings 

 are usually present. 



Measurements : 



(1) (2) (3) (4) (5) (6) (7) (8) (9) 



Length . 32 32 26 21 21 17 16 12 11 mm. 

 Height . 37 35 30 24 22 19 19 14 12 



(1) H. planus zone, Cuxton. (5 7) A quadratus zone, East Harnham. 



(2) Cheveley. (8) M. cor-anguinum zone, Witheringtou. 



(3) ,, Borsted. (9) Uintacrinus band, Devizes Road, Salisbury. 



(4) A. quadratus zone, Whaddon railway cutting, 



near Salisbury. 



Affinities. This species is distinguished from Lima Hoperi by having a smaller 

 apical angle, by being relatively higher and shorter, with the valves less convex, 

 the anterior area relatively smaller, the entire surface of the shell always orna- 

 mented, and the grooves usually deeper. 



The specimen figured by d'Orbigny as Lima Mantelli is similar in form to some 

 examples of L. cretacea, but d'Orbigny states that the furrows are shallow and 

 without pits. A specimen, however, in the d'Orbigny Collection at Paris shows 

 pits in the grooves. 



Lima Iseviuscula, Sowerby (in Dixon) is probably a small example of this 

 species, but its locality and horizon are not stated. 



One of the specimens from the Planer-kalk of Strehlen figured by Geinitz 

 (1872) as L. Hoperi (fig. 11) agrees very closely with this species. 



Distribution. Zone of Terebratulina of Winchester. Zone of Holaster planus of 

 Twyford and Cheveley. Zone of Micraster cor- test udinarium of Borstal and 

 Cuxton. Zone of M. cor-anguinum of Micheldever, Witherington and Camp Hill 

 (South Wiltshire). Zone of Marsupites of Highfield. Uintacrinus band of Devizes 

 Road (Salisbury). Zone of Actinocamax quadratus of Winchester, East Harnham, 

 West Harnham, and Milford (Salisbury). Zone of Belemnitella mucronata of 

 Norwich. Chalk of Trimingham. 



