PRODUCTUS. 167 



age the tubercules became closer and closer, until converted into ribs, the posterior half of the 

 valves usually preserving the characters of the young shell. Martin describes the spines as 

 pointed backwards towards the beak, but this observation has already been shown by Prof, 

 dc Koninck and M'Coy to have been erroneous, their direction being similar to that of 

 other Producta. P. laanspina of Phillips has been drawn from a large example of 

 Martin's species, and the P. spinulosa, Phillips (but not of Sow.), would appear to be like- 

 wise referable to the same species. 



P. aculeatus is a common shell in many localities. In England, it occurs in Carboniferous 

 limestone at Bakewell, Buxton, and Chrome Hill, Longnor, in Derbyshire ; at Settle, in 

 Yorkshire ; Bolland, in Westmoreland ; Lovvick, Northumberland ; in the middle limestone 

 of Pool wash, Isle of Man, &c. In Scotland, at Calderside ; High Blantyre, in Lanarkshire ; 

 Orchard Quarry, Thornliebank, Renfrewshire ; at West Broadstonc, Beith, in Ayrshire ; 

 as well as at Craigie, near Kilmarnock, and Auchenskey, near Dairy, in the same county. 

 In Ireland, in limestone at Lisnapaste, Howth, Old Leighlin, Little Island, and Windmill. 



On the Continent, it occurs at Vise, in Belgium. In Russia it has been found in several 

 localities, such as in the neighbourhood of Buregi, Government of Nowgorod, as well as 

 at Cosatchi-Datchi, on the Oriental side of the Oural, to the east of Minsk, &c. 



Productus Youngianus, Dau. PI. XXXIII, figs. 21 — 23. 



Prodtjctus Youngianus, Dav. Mon. of Scottish Carb. Brach., pi. ii, fig. 26, and 



pi. v, fig. 7, 1861. 



Spec. Char. Shell longitudinally oval ; hinge-line shorter than the width of the shell. 

 Ventral valve regularly arched, convex, and without sinus ; auriculate expansions very 

 small ; beak incurved and comparatively large, not overlying the hinge-line except quite 

 at its attenuated extremity. Dorsal valve very concave, following closely the curves of the 

 opposite one. Surface in both valves ornamented with numerous small, rounded ribs, of 

 which a certain number are due to intercalation, and from which, at short distances, 

 project slender, tubular spines, more widely scattered in some specimens than in others ; 

 the valves are also covered with irregular, undulating, squamiform, concentric expansions, 

 which overlap each other very numerously in some examples, sparingly in others. In the 

 interior the muscular and reniform expansions are similar to those of other Producta. 

 Dimensions variable ; two British examples have measured — 



Length 13, width 9, lines. 

 9 G 1 



Obs. This shell appears distinguishable from P. aculeatus by its more regularly oval 



prickles few, scattered, very minute, short, appressed, or squeezed flat to the surface, and pointing back- 

 wards or towards the beak. The beak small and hooked It is found near Bakewell 



and Buxton." 



