ORDOVICIAN BRACHIOPODA 153 



5 mm antero-medially of the umbo where they arose, and numbered 4 in the sulcus 

 and 8 on each flank. The apsacline interarea was relatively short and curved, and 

 the open delthyrium was flanked by small teeth supported by the walls of a sessile 

 spondylium extending anteriorly for 37% of the length of the valve. 



In the absence of a complementary brachial valve, the identification of the remains 

 of the pedicle valve as Parastrophinella is provisional. Furthermore, the valve is 

 quite different from older Parastrophinella found in Shropshire and Wales with their 

 weak sulci and smooth umbonal regions. More material is, therefore, required not 

 only to indicate the specific affinities of the stock but also to verify the generic status 

 of the specimen. 



Order RHYNCHONELLIDA Kuhn 1949 



Superfamily RHYNCHONELLACEA Gray 1849 



Family TRIGONIRHYNCHIIDAE McLaren 1965 



ROSTRICELLULA Ulrich & Cooper 1942 



Rostricellula sparsa Williams 



(PI. 27, figs. 3, 4, 7) 



1963 Rostricellula sparsa Williams : 467. 



Diagnosis. Small, relatively wide Rostricellula with 2 costae, averaging 0-4 mm 

 thick 2 mm anterior of the umbo, on a well-developed fold two-fifths as wide as the 

 length of the brachial valve, and 4 to 6 costae on each of the lateral slopes. 



Description. Small, biconvex, subtriangular Rostricellula with a brachial valve 

 slightly less long than wide (96% for 2 valves) and 15% as deep as long, and a pedicle 

 valve slightly less than one-quarter as deep as long, dorsal fold (and ventral sulcus) 

 strongly developed up to 40% as wide as the length of the brachial valve and rounded 

 in transverse profile with evenly convex lateral slopes ; rostrate with high curved 

 ventral umbo and inconscpicuous dorsal umbo, apical angle about 100°, nature of 

 deltidial plates unknown ; radial ornamentation exclusively costate with 2 rounded 

 costae on the fold, averaging 0-4 mm in wavelength, 2 mm anterior of the umbones of 

 4 brachial valves, and 4 to 6 on the lateral slopes. 



Ventral interior with small teeth supported by slightly divergent dental plates 

 extending anteriorly for about one-eighth the length of the valve ; muscle field 

 unknown. 



Hinge-plate of dorsal interior small, divided by septalium extending forward for 

 an average of 8% the length of 4 brachial valves, median ridge low, rounded but 

 developed for about two-fifths the length of the valve ; details of crura and muscle 

 scar unknown. 



Figured material. 



length width (mm) 



External and internal moulds of brachial valve (BB 35584a, b) 3-5 3-5 



External and internal moulds of pedicle valve (BB 35585a, b) 3-0 - 



