FROM NORTHWESTERN EUROPE 53 
although still only poorly preserved, appeared to show no notable differences from 
those described above for T. obtrita. 
DIsTRIBUTION. T. acuticosta is one of the most common species in the Lower 
Calcareous Grit of Yorkshire but, according to Arkell (1933), it has only been 
recorded from two localities in the south of England, namely, at Catcombe, near 
Lyneham, and in one of the Kent borings. 
OccuRRENCE. The Lower Calcareous Grit appears to be very similar to the 
“ Terrain a Chailles ’’, as developed in the cordatum and lower tvansversarium zones 
of northern France, with the exception of the abundance of “ Spongia paradoxica”’ 
(=the trace fossil Thalassinoides teste Ager), as seen at Filey Brigg. It would 
appear that the environment represented is again of the nearshore, high energy type. 
Subfamily ACANTHOTHYRIDINAE Schuchert, 1913 
Genus ACANTHOTHIRIS Orbigny 
1850 Acanthothiris Orbigny, 323. 
1875 Acanthothyris Orbigny: Paetel, 1. 
1877. Acanthothiris Dall, 11. 
1886 Gruppe der Spinosen Rothpletz, 93. 
1889 Acanthothyris Orbigny: Buckman and Walker, 41. 
1894 Acanthothyris Orbigny: Hall and Clarke, 836. 
1914 Acanthothiris Orbigny: Buckman, 2. 
1917 Acanthothyris Orbigny: Rollier, 74. 
1918 Acanthothiyvis Orbigny: Buckman, 70. 
1929 Acanthothiris Orbigny: Schuchert and Le Vene, 26. 
1936 Acanthothyris Orbigny: Muir-Wood, 27. 
1960 Acanthothiris Orbigny: Ager, 157. 
1960 Acanthothyris Orbigny: Makridin, 256. 
1963 Acanthothiris Orbigny: Seifert, 168. 
19656 Acanthothiris Orbigny: Ager, Horr. 
Type SPECIES. Terebratulites spinosus Schlotheim, designated by Rollier (1917). 
This is regarded by the author as a synonym of Anomia spinosa Linnaeus (1767) and 
is discussed below. 
EMENDED DIAGNOSIS. Small to medium sized sub-pentagonal or laterally oval 
rhynchonellids ; biconvex ; uniplicate with low dorsal fold ; many well developed 
ribs, several of which bifurcate ; test covered by hollow spines which arise from the 
crests of the ribs ; beak small and erect or slightly incurved ; well developed groove 
(“ pedicle trough ’’) running from posterior of pedicle opening to tip of beak ; fairly 
strong median septum present ; crura radulifer. 
STRATIGRAPHICAL RANGE. ? Aalenian, Bajocian—Bathonian/basal Callovian. 
DESCRIPTION. External characters. The larger acanthothirids tend to be more 
globose than the smaller ; the brachial valve is more inflated than the pedicle. 
The many well marked, rather shallow, sub-rounded ribs tend to bifurcate laterally 
and from their crests arise the long, slender, hollow spines which cover the test. 
There is a slight fold on the dorsal valve and a rounded uniplication in the anterior 
commissure. The beak is relatively small and sufficiently incurved to obscure the 
