LIMA. 23 



regular curve. Unibones small, cloric together. Apical angle usually about 1(30°, 

 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 gi'owth-rings 

 are usually present. 



Meatmrcmeids : 



(fi) (V) (8) (9) 



17 K) 12 11 mm. 

 lU 10 14 12 „ 



(1) H. 2)lanus zoue, Cuxton. (5 — 7) A quaih-atus zone, East Haniliain. 



(2) „ „ Cheveley. (8) M. cor-anguinum zone, Willieriiii,'tou. 



(3) ,, ,, Borsteil. (9) Uintacriiius baud, Devizes Road, Salisbury. 



(4) A. quad rat U!< zone, Wbadduu railway cuttiu*,', I 



near Salisbur 



V. 



Affinities. — This species is distinguished from Linui ILqicri by having a smaller 

 apical angle, by being relatively higher and shortei-, 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 Limd Mnidelli is similar in foi'in 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 Iseviusciila, 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 Plauer-kalk of Strehlen figured by Geinitz 

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



Dislrihution. — Zone of Terehratulina of Winchester. Zone of Holuder planus of 

 Twyford and Cheveley. Zone of Micraster cor-testudinariunt of Borstal and 

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

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

 Road (Salisl)my). Zone of Arfiiiofnina.r ipuHlyiitHs of Winchester, East Harnham, 

 West Harnham, and Milford (8alisl>ury). Zoue of Bclemnitella mucronata of 

 Norwich. Chalk of Trimingham. 



