118 



L.R.M. COCKS AND ZHAN REN-BIN 



exopunctae are visible in lines along the rib crests, with a few 

 additional exopunctae sporadically distributed on the rib slopes. 



Ventral interior. Small teeth supported by a pair of very short, 

 subparallel dental plates. Poorly impressed muscle field about 28% 

 as wide as the shell and open anteriorly. Strong crenulations along 

 the peripheral area of both valves about one quarter of the shell 

 length, which form broad, flat to weakly hollowed, scalloped ridges 

 separated by narrow deep grooves. 



Dorsal interior. Cardinalia about one fourth as wide and one sixth 

 as long as the shell; small cardinal process limited to the posterior 

 part of the narrow but weakly elevated notothyrial platform, and 

 connected with the posterior ends of the brachiophores on both 

 sides. Well-developed brachiophores triangular at their base, highly 

 projecting anteriorly and ventrally at 90-1 10° to one another, and 

 supported for their posterior one-third by thin subparallel plates. 

 Weakly-impressed subquadrate muscle field just in front of the 

 cardinalia, composed of two pairs of adductor scars on either side of 

 a low and wide myophragm which becomes wider anteriorly to- 

 wards the shell margin; the posterior scars always larger than the 

 anterior pair. 





L 



W 



LAV 



W i 



W,AV 



N 



B37668, dorsal valve 



4.7 



5.5 



0.85 



1.4 



0.25 



18 



B37669, dorsal valve 



3.0 



3.7 



0.81 



0.9 



0.24 



18 



B37670, dorsal valve 



2.4 



3.3 



0.73 



0.9 



0.27 



18 



B37682, ventral valve 



4.5 



6.4 



0.70 



1.8 



0.28 



15 



■B37702, dorsal valve 



4.7 



5.3 



0.88 



- 



- 



18 



.B37705, ventral valve 



4.2 



5.2 



0.81 



1.5 



0.28 



15 



■29665, dorsal valve 



6.6 



9.1 



0.73 



2.6 



0.28 



- 



Discussion. The species irravadica was named by Reed (1906) 

 within the genus Orthis for some small specimens from the 

 Naungkangyi Group at several localities in the Northern Shan 

 States. The illustrated exteriors and ventral interiors (Reed 1906: pi. 

 4, figs 15-22) are similar to our specimens from the same area and 

 are assigned to Saucrorthis especially on the ribbing and cardinalia. 

 Orthis pustulifera Reed (1936: 18, pi. 1, figs 7-14; pi. 2, fig. 3), from 

 rocks corresponding to the Naungkangyi Group at Thitteikkon and 

 Konleau, Southern Shan States, is much like irravadica in its 

 external characters and cardinalia, but it has better-preserved 

 exopunctae and stronger dorsal muscle bounding ridges and dental 

 plates. The species is questionably included as a junior synonym of 

 irravadica. The material identified by Reed (1932, 1 936 ) as Yeosinella 

 consignata Reed consists of some dorsal valves from rocks corre- 

 sponding to the Naungkangyi Group at Ye-o-sin in the Southern 

 Shan States which seem identical to our specimens of irravadica. 

 No ventral valves of consignata are known, but should they also 

 prove to be the same as irravadica, then Yeosinella would become a 

 senior synonym of Saucrorthis. 



Saucrorthis, previously thought endemic to South China, is 

 recorded here from outside it for the first time. The type species, S. 

 minor (Xu, Rong & Liu 1974: 151, pi. 66, figs 1^1), from the 

 Shihtzupu Formation (early Caradoc) at Zunyi, Guizhou Province, 

 differs from irravadica in having a smaller subquadrate shell, nar- 

 rower divergent brachiophores (about 75° as compared with 90-1 1 0° 

 in irravadica), much stronger peripheral crenulations and more 

 developed dental plates. Sulevorthis, a small orthid named by 

 Jaanusson & Bassett (1993: 40) with its type species Orthis 

 lyckholmiensis Wysogorski from the Lyckholm Beds ( Vormsi Stage, 

 late Caradoc) of Korgessaare, Hiiumaa, Estonia, is very similar to 

 Saucrorthis externally, but its strong cardinal process is elongate, 

 occupies the entire notothyrial cavity and is separated from the 

 brachiophores completely, and no notothyrial platform is developed. 



Among all the species assigned to Sulevorthis by Jaanusson & 

 Bassett (1993: 38), Orthambonites parvicrassicostatus (Cooper 

 1956: 309. pi. 35B. figs 11-25) from the Benbolt Formation 

 (Porterfieldian, early Caradoc?) ofVirginia, USA -andOrthambonites 

 humilidorsatus (Wright 1964: 160.pl. 1 . figs 1-12) from the Portrane 

 Limestone (Caradoc) of Ireland are the species of Sulevorthis most 

 similar externally to our present material, particularly in the pres- 

 ence of exopunctae. 



Family SKENIDHDAE Kozlowski. 1929 

 Genus SKENIDIOIDES Schuchert & Cooper. 1931 



Skenidioides sp. 



71936 Skenidioides cf. billingsi Schuchert & Cooper; Reed: 68, 

 pi. 2, figs 8, 8a. 



Material and locality. One ventral valve (internal and exter- 

 nal moulds), BB 37594, from the equivalents of the Upper 

 Naungkangyi Group at Linwe (Locality AM 78), Southern Shan 

 States. 



DISCUSSION. A single broken shell 3.7mm long and 4.7mm wide, 

 with radial costae branching only once within one-third of the shell 

 length and 4 per mm on the shell anterior, a very high interarea and 

 small teeth, is typical of Skenidioides. Reed described two species of 

 this genus from the Southern Shan States, Skenidioides cf. oelandicus 

 Wiman from the Naungkangyi Group at Nam Wabya (Reed 1936: 

 30, pi. 2, figs 18-21) and Skenidioides cf. billingsi Schuchert & 

 Cooper from the Bawzaing Horizon (contemporary with the 

 Naungkangyi Group) at Sinchaung (Reed 1936: 68, pi. 2, figs 8, 8a). 

 S. cf. oelandicus does not appear from Reed's illustrations to be a 

 Skenidioides because the ventral interarea is far too small. S. cf. 

 billingsi is represented in Reed's material by a single ventral internal 

 mould which may or may not be a Skenidioides and the same as the 

 present specimen; it is poorly preserved. 



Superfamily DALMANELLOIDEA Schuchert, 1913 



Family DALMANELLIDAE Schuchert, 1913 



Subfamily DALMANELLINAE Schuchert, 1913 



Genus ONNIELLA Bancroft, 1928 



Onniella chaungzonensis (Reed. 1906) PI. 2, figs 6-10 



1906 Orthis (Dalmanella?) chaungzonensis Reed: 61, pi. 4, figs 



7-14. 

 1906 Orthis (Dalmanella) testudinaria Reed: 60, pi. 4, figs 25- 



26. 

 1915 Orthis (Dalmanella) testudinaria shanensis Reed: 9, pi. 2. 



figs 6-7. 9-10. 



Material and localities. One dorsal and one ventral valve 

 (both internal and external moulds) from the Naungkangyi Group in 

 theYadanatheingi area (Locality AMI ); three dorsal valves (internal 

 and external moulds), and five ventral internal and four external 

 moulds from the Li-lu Formation (equivalent to the Upper 

 Naungkangyi Group) at Ta-Pangtawng (about 10 km east of 

 Longtawkno, Locality YA454.1), both in the Northern Shan States. 

 One dorsal internal mould from the equivalents of the Upper 

 Naungkangyi Group at Linwe (Locality AM77). Southern Shan 

 States. 



