SPONDYLUS. 12S 



Non 1842. Spondylus latus, A. Leymerie. Mem. Soc. gcol. de France, vol. v, p. 10, 



pi. vi, fig. 10. 



Description. — Shell oval, rounded, more or less oblique, but sometimes nearly 

 equilateral, of moderate size or small, height and length nearly equal. Right valve 

 usually attached by its entire surface, and bearing concentric spiny lamellae ; when 

 part of the valve is not attached it is ornamented with numerous radial ribs ; the 

 whole of the interior also shows numerous small radial ribs. 



Left valve inflated, sometimes with undulating surface; growth-lines few and 

 not strongly marked ; the radial ribs are numerous, small, regular, flattened or 

 rounded, without spines, and of equal size, except when new ribs are occasionally 

 introduced ; the ribs are separated by grooves of the same or less width, and in 

 these are seen very faintly marked transverse ribs, which sometimes pass on to the 

 radial ribs. Umbo small, pointed. Near the umbo some of the radial ribs, at 

 regular intervals, are stronger than the others, and bear short spiny processes. 

 Ears smooth. 



Measurements : 



(1) (2) (3) (4) (5) (G) (7) (8) (9) (10) 



Length . . . 25 25 24 23 21 26 34 40 43 23 mm. 

 Height ... 26 25 24 23 20 27 36 37 39 23 „ 



(1 — 4) zone of A. quadratus. East Harnham, Salisbury. 

 (5) ,, ,, West Harnliam, Salisbury. 



(6, 7) zone of M. cor-anguinum, Graveseud. 



(8, 9) zone of H. suhglobosus, Cherry Hinton ; (8) is the tyjie of S. sequicostatus, Eth. 

 (10) Lower Chalk, Fulbourn Asylum. 



Affinities. — The numerous smooth ribs serve to distinguish this species. >S'. 

 striatus, Sowerby, from the Warminster Greensand, etc., is a much larger form, 

 shorter in proportion to its height, and with the umbonal region more produced. 



The form from the Lower Chalk, described by Etheridge as S. aequicostatus^ 

 cannot, I think, be separated from this species; the type (PI. XXII, fig. 1) 

 appears to differ somewhat from ;8'. latus, but this is on account of its being an old 

 individual; other smaller examples found on the same horizon are inseparable 

 from S. Jatiis found in higher zones of the Chalk. The Lower Chalk forms are in 

 several cases somewhat larger than any that I have seen in the Middle or Upper 

 Chalk. Two specimens from the Chalk Marl of Dover and Folkestone probably 

 belong to this species, but more examples are needed before a definite determiuation 

 can be made. 



Tijpes. — The type, from the Chalk of Lewes, and the specimen figured by 

 Dixon, are in the British Museum. I have not seen the types of Diancliora ohliquu, 

 Mantell, which came from Lewes and Brighton ; nor his figured specimen of S. 

 latus. The type of S. usquicostatus, Etheridge, is in the Woodwardian Museum. 



