588 ME. LINSDALL EICHARDSON ON ["Nov. I906, 



it is with this stage of D. subtrigonale that the present species has 

 the greatest affinity. D. subovatum, however, is from a deposit of 

 marmorece-Birchi (?) date, and is a very much smaller species than 

 D. subtrigonale — an armatum-zowe fossil. The former has a sub- 

 ovate transverse section, and, from the few specimens which it has 

 been possible to examine, this seems a fairly-constant character : the 

 exception being, as already stated, when the dorsal side is flattened. 

 In D. subtrigonale the section is triangular, with a blunt and 

 noticeable ventral carina in the neanic stage. 



The specimen figured as Dentalium Hmatulum by Tate in ' The 

 Yorkshire Lias ' is between 9 and 10 millimetres in length : the 

 diameter of the anterior end measuring slightly over 1 mm., and 

 that of the posterior end 075 mm. The transverse linese, on the 

 whole, are much finer than in D. subtrigonale. 



Terquem's remarks on the species that he dealt with from the ; gres 

 infra-liasique de Hettange,' which he hesitatingly referred to 

 d'Orbigny's Dentalium compression, were as follows [translation] : — 



' This shell, found in a crypt of Saxicava, is very slender and fragile, strongly 

 compressed, shiny, subarcuate, and ornamented with very fine, closely-set stride, 

 visible only with a strong lens. — Yery rare.' 



'Observation. — It is difficult to point out a specific character for shells 

 the shape of which presents so little variation ; for this reason we have adopted 

 the denomination of M. d'Orbigny, although it has been applied to a species 

 from the Middle Lias.' 



Prom this there can be little doubt that Dentalium compressum, 

 Terquem, is referable to the present species. Brauns, however, 

 regarded Terquem's shell as being the same as D. etalense, Terq. & 

 Piette. In his notes he comments upon the fact that D. etalense, 

 Terq. & Piette, is not compressed, and observes that this charac- 

 teristic feature is also wanting in D. compressum, Terquem. But 

 it is not : Terquem distinctly says that this fossil is ' strongly 

 compressed.' 



With regard to the specimens identified with Dentalium com- 

 pressum, d'Orbigny, by Terquem & Piette, those from the ' calcaire 

 a A. bisulcatus [hemera rotiformis ?] de Jamoigne,' and the 4 gres 

 a A. angulatus de Saint Menge,' probably belong to D. subovatum ; 

 while those from the ' gres a B. acutus d'Etales et de Maubert,' 

 may belong to D. trigonale, Moore. Brauus would refer these also 

 to D. etalense. 



Dentalium subquadratum, sp. nov. (PI. XLY. fig. 8.) 



T.f. Transverse section, PL XLV, fig. 8. 

 T.l. Honeybourne (clay-pit?), near Evesham. 

 H. ' Lower Lias.' Sinemurian. 

 rj. Tzcrneri (about). 

 Colin. Slatter, Nat. Hist. Mus. (G. 10807). 



Diagnosis. — Shell small, slightly curved, test thin ; transverse 

 section subquadrate exteriorly and interiorly ; surface smooth. 

 The posterior portion is more angular than the anterior, in which 

 the dorsal margin is slightly broadened. Length = 11 millimetres ; 

 diameter of anterior end = about *5 mm. 



