Vol. 62.] LIASSIC DEXTALIID.E. 587 



advisable that the particular form referred to by an author should 

 be clearly indicated. Thus Dentalium parvulum proper may be 

 understood to embrace those thin-walled shells which have a 

 circular to slightly-elliptical transverse section — the commonest 

 form ; D. parvulum a those with an elliptical section ; and D. parvu- 

 lum ft the thick-walled forms, with a very perfect circular section. 

 The specimens mentioned in the subjoined list have all passed 

 through my hands, and the majority are in my collection : — 



Dentalium parvulum. — margaritati 1 Chipping Norton, Oxfordshire (form j3: 

 identified by Slatter with D. minimum, Strickland-Buckruan) ; Valdani, 

 Leckharapton Boad clay-pits, Cheltenham (Holl Colin., Nat. Hist. Mus., etc.) ; 

 Battledown Brickworks, Cheltenham ; Clay-pit (disused), Hucclecote, near 

 Gloucester ; Jamesoni (about), Bishop's Cleeve Station, near Cheltenham ; armati 

 (& Jamesoni?), railway-cutting, Aston Magna, near Moreton-in-the-Marsh ; 

 armati-Jamesoni, railway-cutting, Toddington, near Cheltenham; armati, Folly- 

 Lane clay-pit, Cheltenham ; oxynoti-armati, Gasworks, Gloucester (& form a) ; 

 Turneri, Honeybourne clay-pit, near Evesham (form /3 : Slatter Colin., Nat. 

 Hist. Mus.); rotiformis, Bengeworth clay-pit, Evesham (forma: Nat. Hist. 

 Mus.) l ; rotiformis ? Aldington Leys, near Evesham (form a : Slatter Colin., 

 Nat. Hist. Mus.) 1 ; marmwece, clay from pond a quarter of a mile north of 

 Bamfurlong, near Cheltenham (form a) ; Birchi ? Besford clay-pit, near Defford, 

 Worcestershire (Slatter Colin., Nat. Hist. Mus.). 1 



Dextalium subovattiac, sp. nov. (PI. XLY, fig. 7.) 



T.f. 1876. Tate, ' The Yorkshire Lias ' pi. x, fig. 18. 

 T.l. Redcar [Yorkshire]. 

 H. 'Lower Lias ' (A. angulatus-zowo) . 

 r\. [marmorece.] 

 Colin. Tate, Museum of Practical Geology, Jermyn Street. 



Syn. 1855. Dentalium compression, Terquem, ' Paleontologie de Hettange ' Mem. 

 Soc. Geol. France, ser. 2, vol. v, p. 280. 

 1865. D. compression, Terquem & Piette, pars ? ' Le Lias Inferieurde l'Est 



de la Prance 'Mem. Soc. Geol. France, ser. 2, vol. viii, p. 67. 

 1876. D. limatulum, Tate, ' The Yorkshire Lias ' pp. 332-33 & pi. x, fig. 18. 



Diagnosis. — Shell small, slightly curved ; transverse section sub- 

 ovate exteriorly, oval interiorly, but becoming more nearly circular 

 in specimens which have a flat or very slightly-convex dorsal side ; 

 surface-ornamentation consisting of fine transverse linese. 



II em arks. — The specimens from the Lower Lias of Redcar 

 identified by Tate with his Dentalium limatulum from the ' Zone of 

 Belemnites acutus,' Cloverly (Shropshire), do not appear to belong to 

 the same species. I have examined what remains of the holotype 

 of Dentalium limatulum, Tate (which is deposited in the Geological 

 Society's Museum), and those specimens from Yorkshire, and find 

 that the transverse section of the former is subpentagonal, while 

 that of the one chosen from the latter series by Tate for figuring in 

 ' The Yorkshire Lias ' is subovate. This feature, however, is better 

 shown in certain topotypes which are preserved in the Museum of 

 Practical Geology, Jermyn Street. 



In those specimens which have a flat or very slightly-convex 

 dorsal side the aperture is nearly circular, and in this condition it 

 resembles certain forms which belong Avithout doubt to a certain 

 stage in the development of Dentalium suhtrigonale (p. 589). Indeed, 



1 These were identified by Slatter as Dentalium minimum. 



