﻿76 MR. T. F. SIBLT ON THE PATJNAL SUCCESSIOX i:?^ THE [Feb. I908, 



(B) BRACHIOPODS. 



Productus. 



Prodtjctus concinnijs, Sow., and Pr. Martini, Sow. 



Eoth these species occur abundantly in D., and D^ in the Midland 

 area. I have examined Sowerby's type-specimens,^ and numerous 

 specimens collected by myself in the Midlands, and the relationship 

 of the two species appears to me to be as follows. 



Typical examples of Productus concinnus and Pr. Jlartini^ which, 

 agree in the nature of their ribbing and in the development of 

 spines on the flanks of the convex valve, differ in the following 

 respects : — In Productus Martini, the convex valve is non-sulcate ; 

 the skirt-like, frontal portion of the valve is greatly developed ; 

 semireticulation is generally inconspicuous ; and the intersection 

 of the two valves is approximately square-shaped. In Productus 

 concinnus^ which is a smaller shell, the convex valve is sulcate ; 

 the skirt-like, frontal portion of the valve is less extensive ; semi- 

 reticulation is strong on the wings, and sometimes extends over 

 the body of the valve ; and the intersection of the two valves is 

 slightly transverse. 



Typical examples of these two species are readily distinguished, 

 and such specimens occur quite commonly ; but intermediate forms, 

 which may be referred indifferently either to one species or to the 

 other, are equally common. The most frequently-occurring of 

 these intermediate types has the greatlj'-developed ' skirt ' of 

 Productus Martini^ with the sulcate form and marked semi- 

 reticulation of Pr. concinnus., and shows a valve-intersection which 

 is sometimes square and sometimes transverse. This intermediate 

 type occurs most commonly in D.,. The typical form of Productus 

 Martini attains its maximum. in the localized D., ' brachiopod-beds,' 

 while the typical Pr. concinnus has its maximum in D3. 



Gens of Productus longisj^inus, Sow. 



Producti belonging to this group range throughout almost the 

 whole vertical extent of D,,, and occur very commonly in Dg, in 

 the Midland area. Many forms are represented. 



Specimens closely similar to the typical form of Productus longi- 

 spinus (Sowerby, ' Min. Conch.' vol. i, 1812, pi. Ixviii, fig. 1; & 

 Davidson, ' Monogr. Brit. Foss. Brachiop.' Palaeont. Soc. vol. ii, 

 1858-63, pi. XXXV, fig. 5) occur in J)^, and more commonly in Dg. 



A form which closely resembles Prod.uctus lobatus, Sow. (' Min. 



^ Now preserved in the British Museum (Natural History), South Kensington. 

 The types of Prodttctns concinnus, figured in Sowerby's ' Min. Conch.' vol. iv 

 (1823) pi. cccxviii, fig. 1, were obtained from Derbyshire. The locality of the 

 type of Productus. Martini (ibid. pi. cccxvii, fig. 2) is not definitely stated ; 

 but Sowerby mentions that the species is ' not uncommon in the Derbyshire 

 Limestone' ; and the specimen was probably obtained from the Midland area, 

 where identical specimens occur in many localities. 



