42 SHELVE DISTRICT 



valves (range 9% to 11%) forward of their posterior margins ; dorsal beak represent- 

 ing the highest point of the brachial valve located, on average, 23% of the length of 

 5 brachial valves (range 15% to 25%) forward of their posterior margins. 



Limbus well defined in both valves except posteriorly where it becomes obscure, 

 other internal features unknown except for the characteristic two lines diverging 

 from the ventral beak. 



Figured material. 



length width (mm) 



Exfoliated exterior of pedicle valve (BB 35596) 2-0 i-8 



Exfoliated exterior of brachial valve (BB 35597) 20 i-8 



Horizon and locality. Spy Wood Grit exposed in Spy Wood Dingle (Grid 

 Ref. SO 281959). 



Discussion. Paterula occurs sporadically throughout much of the Shelve 

 succession, although only 3 samples were available for study and even they were too 

 small for anything but the simplest statistical assessment of variability. They do 

 show, however, that the Shropshire Paterula belong to two distinct species. In the 

 older stock, as represented by the samples from the Hope Shales and Meadowtown 

 Beds, the posterior margin tends to be flattened or truncated, the limbus is well 

 developed and the dorsal beak is submarginal. Such features, with the exception 

 of the first, are also characteristic of P. bohemica, figured by Barrande (1879 : plate 

 152) from the Llanvirnian Sarka Formation of Czechoslovakia. They are not 

 developed in specimens recovered from the Spy Wood Grit which tend to have a 

 limbus becoming obscure anteriorly and especially a dorsal beak located well forward 

 of a rounded posterior margin. The Spy Wood sample is close to P. perfecta Cooper 

 (1956 : 258) from the Pratt Ferry Formation of Alabama except in the strength of 

 the limbus which is continuous in the American species. 



Despite these differences, the Shelve Paterula, provisionally at least, are most 

 appropriately compared with P. bohemica and P. perfecta, the former to embrace 

 specimens from the Mytton Flags to the Rorrington Beds inclusive, the latter shells 

 occurring in the Spy Wood Grit and Aldress Shales. 



Order ACROTRETIDA Kuhn 1949 



Suborder ACROTRETIDINA Kuhn 1949 



Superfamily ACROTRETACEA Schuchert 1893 



Family ACROTRETIDAE Schuchert 1893 



APSOTRETA Palmer 1955 



Apsotreta sp. 



(PI. 6, figs. 14, 15) 



The complementary moulds of an acrotretid pedicle valve (BB 35565a, b), from 

 the Mytton Flags exposed near Wood House (Grid Ref. SJ 338003), are the sole 



