SPONDYLUS. 123 
Non 1842. Sponpytus tatrus, A. Leymerie. Mém. Soe. géol. de France, vol. v, p. 10, 
pl. 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 lamelle ; 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, pomted. 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) (8) (4) (5) (6) (7) (8) (9) (0) 
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) 33 West Harnham, Salisbury. 
(6, 7) zone of M. cor-anguinum, Gravesend. 
(8, 9) zone of H. subglobosus, Cherry Hinton; (8) is the type of S. equicostatus, Eth. 
(10) Lower Chalk, Fulbourn Asylum. 
Affinities —The numerous smooth ribs serve to distinguish this species. SN. 
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 8. xquicostatus, 
cannot, I think, be separated from this species; the type (Pl. XXII, fig. 1) 
appears to differ somewhat from NS, /atus, but this is on account of its being an old 
individual; other smaller examples found on the same horizon are inseparable 
from S. latus 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 determination 
ean be made. 
Types.—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 Dianchora obliqua, 
Mantell, which came from Lewes and Brighton; nor his figured specimen of S. 
latus. The type of S. equicostatus, Etheridge, is in the Woodwardian Museum. 
