RHYNCHONELLIDE BRACHIOPOD 1SOPOMA TORLEY 



71953 Isopoma lummatoniensis (Davidson); Rzhonsnitskya: 176, 

 pi. 10, figs 14, 15. 



TYPE SPECIMEN. BB 6184, figured by Davidson (1865: pi. 14, fig. 

 14), is here selected lectotype (Fig. 9a-d). 



COMMENT. Davidson (1865), described a series of quarries at 

 Lummaton, about 3 miles north of Torquay, Devon. He referred to 

 the beds as the Stringocephalus Burtini Beds. The Lummaton Shell 

 Bed is part of this series of late Givetian fossiliferous limestones. 

 Davidson ( 1 882: 1 1 ) said Rigaux (1878) had recorded Rhynchonella 

 lummatoniensis at Ferques, France. However, the extensive ecologi- 

 cal study by Wallace (1966; 1969) in that area did not record the 

 species, so we are doubtful about Isopoma occurring at Ferques. 



The species is characterized by its high ventral sulcus containing 

 a single rib and the deep body cavity; the dorsal valve has a 

 corresponding long narrow median groove. Davidson ( 1 865: pi. 14, 

 fig. 15) figured a second syntype of Rhynchonella lummatoniensis 

 which is less deep-bodied and has two ribs in the ventral sulcus. This 

 might be conspecific with the lectotype, but it recalls the similarly 

 shallow specimen of/, maymyoensis described below. Large collec- 

 tions might reveal whether these shallower specimens with more 

 ribs are really conspecific. 



Rzhonsnitskya (1953: 176, pi. 10, figs 14, 15) recorded and 

 illustrated /. lummatoniensis from the Frasnian of the Kuznetsk 

 Basin, Russia, but internal structures of these specimens are very 

 poorly known and generic assignment remains in doubt. 



Isopoma maymyoensis sp. nov. 



159 

 Figs 12-14,20 



1969 Uncinulus subsignata Reed; Anderson etal:. 137.pl. 5, figs 

 18-21 (non figs 22-3 1 ). 



Etymology. The species is named from Maymyo, Burma, the 

 region from which the material was collected. 



Type specimen. The holotype (BB 55546; figured Anderson, 

 Boucot & Johnson, 1969: pi. 5, figs 18, 19) is from the Padaukpin 

 Limestone (late Eifelian to early Givetian), Padaukpin, 10 miles NE 

 of Maymyo, Central Burma. 



Diagnosis. Isopoma with relatively shallow body cavity and 

 weakly developed uniplication modified by 1-3 short ribs within the 

 sulcus; an additional pair of ribs may occur laterally; hinge plates 

 well separated both medially and from the dorsal valve floor. 



Comment. Anderson et o/.'s (1969) description of Uncinulus 

 subsignata included smaller specimens which are here called 

 Isopoma maymyoensis, as well as larger specimens (Anderson et al. , 

 1969: pi. 5, figs 22-31) which we accept as Nalivkinaria subsignata 

 (see Mohanti, 1972: 166). The age of the Isopoma specimens, 

 together W\W\Nalivkinaria, was originally given as probably Eifelian, 

 but we extend the age of the beds into the Early Givetian (Mohanti 

 & Brunton, 1992: 11). Ecologically Isopoma maymyoensis thrived 

 in a shallow marine subtidal benthic level-bottom environment and 

 the associated carbonates contain a variety of shelly fossils. 



Figs 12, 13 Isopoma maymyoensis sp. nov., late Eifelian to lower Givetian, Padaukpin Limestone. Padaukpin. Burma. 12a-d, Holotype; dorsal, ventral, 

 anterior and lateral views (note that the umbo is broken): BB 55546, x 4. 13a-d, dorsal, ventral, anterior and lateral views, x 4; 13e, detail of part of the 

 dorsal valve, BB 55547. x 10. 



Fig. 14 Isopoma maymyoensis sp. nov. Sections at the sockets and hinge plates and anteriorly through the crura. Padaukpin Limestone. Burma, BB 55547. x 9. 



