"Vol. 62.] FAUXAL SUCCESSION IX THE CARBONIFEROUS OF RUSH. 307" 



The three fundamental types are : — 



Productus pustulosis, Phil., 1 Pr. Jimbriatus, J. de C. Sow., 2 and 

 Pr. punctatus (Martin). 3 Martin's type of Pr. punctatus and 

 Phillips's type of Pr. pustulosus agree in the form of the two 

 valves, and in the possession of numerous concentric bands, 

 separated by sharp grooves. 



They differ completely in the nature and distribution of the 

 spine-bases. In the type of Pr. pustulosis, the spine-bases are 

 broad, well-spaced pustules arranged in concentric rows, each row 

 ornamenting one of the concentric bands. In the type of 

 Pr. punctatus the spine-bases are extremely numerous, small, and 

 closely-packed, three to four concentric rows ornamenting each 

 concentric band. (The spines which compose the uppermost row 

 on each band are always larger than those of the lower rows.) 



The type of Pr. Jimbriatus, J. Sow., has the following characters: — 



(a) Pedicle- valve. — Form elongate and continuously convex, with a short 

 hinge-line and arched beak. A small number of broad concentric ridges, 

 separated by broad concentric depressions. Broad, well-spaced spine-bases ; a 

 single concentric row of spines ornamenting each concentric ridge. 



(b) The brachial valve is continuously concave. 



Variation (in so far only as specimens cited in this paper are 

 concerned) : — 



(1) Of Pr. pustulosis, in a direction diverging from the fimbriate 

 and punctate groups. — Here is included Pr.pyocidiformis,fe Kon., 4 the 

 type of which exhibits irregular concentric wrinkles, feebly separated 

 by irregular concentric ruts. Pyxidiform variants of Pr. pustulosus 

 are not uncommon in the Ci/athaxonia-Beds of the Rush sequence 

 and in the Curkeen Limestone. They are intermediate between 

 Pr. pustulosus and Pr. pyocidiformis, the concentric banding being 

 irregular, but the concentric grooves distinct. 



(2) Of Pr. pustulosus, towards Pr. Jimbriatus. — All such variants 

 may be included under the term Pr. Jimbriato-pustulosus. Here 

 is included Pr. ovalis, Phil., 5 the type of which has an elongate 

 fimbriate form (flattened over the median area of the pedicle-valve); 

 concentric grooves are very indistinct, and the spine-bases narrow. 

 One of the forms from the Curkeen Limestone approaches very 

 close to Pr. ovalis, differing only in the more marked separation 

 of the concentric bands. 



(3) Of Pr. Jimbriatus, towards Pr. punctatus (= Pr. punctato- 

 Ambriatus). — Here is included Pr. elegans, M'Coy, 6 the type of 

 which is, in all respects of form and banding, a pure fimbriate 



1 « Geology of Yorkshire ' vol. ii (1836) pi. vii, fig. 15. 



2 'Min. Conch.' vol. v (1825) pi. cccclix, fig. 1. 



3 ' Petrificata Derbiensia ' 1809, pi. xxxvii, fig. 6. 



4 ' Monographic du Genre Productus,' Kecherches sur les Animaux fossiles, 

 pt. i (1847) pi. xvi, fig. 2. 



3 ' Geology of Yorkshire ' vol. ii (1830) pi. viii, fig. 14. 

 G ' British Palaeozoic Fossils ' 1855, pi. iii H, fig. 4. 



