152 SHELVE DISTRICT 



Description. Small, biconvex, subtriangular Parastrophinella with a brachial 

 valve averaging 93% as wide as long and 29% as deep as long (for 4 and 3 valves 

 respectively) and a mean depth of 23% relative to the length of 3 pedicle valves, 

 transverse profile evenly convex with steep lateral slopes, longitudinal profile evenly 

 convex to anteriorly geniculate, dorsal fold and ventral sulcus faintly and sporadically 

 developed ; rostrate with depressed palintropes extending antero-laterally for up to 

 35% OI * ne maximum width of the shell, delthyrium and notothyrium open ; shell 

 smooth for an average of 37 mm anterior of the umbones of 3 specimens, delayed 

 costation consisting of rounded costae with a mean wavelength of 0-56 mm between 

 5 and 6 mm anterior of the umbones of 7 brachial valves and numbering 10 to 14 in 

 1, 2, 1, 2 and 1 brachial valves respectively between 5 and 7 mm long. 



Ventral interior with small teeth and well-developed spondylium sessile posteriorly 

 but supported anteriorly by a median septum extending forward for an average of 

 45% °f the length of 3 pedicle valves. 



Dorsal interior with subparallel outer plates separated by less than one-tenth the 

 maximum width of the brachial valve and extending forward for a mean proportion 

 of 40% of the length of 4 valves ; elongately oval adductor scars impressed on either 

 side of the outer plates for an average of 56% of the length of 3 valves. 



Type material. 



length width (mm) 

 Holotype External and internal moulds of pedicle valve 



(BB 35598a, b) 7-0 8-5 

 Paratypes External and internal moulds of brachial valve 



(BB 35599a, b) 6-o 5-8 



Internal mould of brachial valve (BB 35600) 5-0 5-2 



Internal mould of pedicle valve (BB 37107) 5-5 5-0 



Internal mould of brachial valve (BB 37108) 7-5 7-0 



Type horizon and locality. Spy Wood Grit exposed 1100 yds NNE of 

 Rorrington (Grid Ref. SJ 303015). 



Discussion. The Spy Wood Grit porambonitacean is an early species of Para- 

 strophinella which is like the Upper Llandeilo P. costata MacGregor (1961 : 199) 

 except for its significantly fewer, coarser ribs, its relatively greater length and the 

 vestigial nature of its fold and sulcus. These differences are important enough to 

 merit systematic recognition. 



Parastrophinella sp. 



(PI. 28, figs. 14, 15) 



Incomplete external and internal moulds (BB 35461a, b) of a pedicle valve, 

 collected from the Hagley Volcanics in the roadside quarry 150 yds. north of Church 

 Stoke Hall (Grid Ref. SO 274942), probably represent Parastrophinella. The valve, 

 which was 13-5 mm long, was 85% as long as wide and 25% as deep as wide with a 

 persistent flat-bottomed sulcus about 60% as wide as long and evenly convex flanks. 

 Radial ornamentation consisted of rounded costae about 0-8 mm in wavelength, 



