60 
N. W. ARCHBOLD 
dorsal valve; same locality and collector as holo- 
type. 
Size ranges. Maximum width 5.7-14.9 mm; hinge 
width 5.5-14.2 mm; ventral length 6.5-10.6 mm; dor¬ 
sal length 4.3-9.3 mm. 
Diagnosis. Small Neochonetes (Sommeriella). 
Ventral sulcus weakly developed; dorsal fold low 
but distinct. External ornament of fine capillae, 
on average numbering 3 per mm at 6 mm from 
umbones. 
Description. Length of shell just over two-thirds 
of maximum width. Maximum width just an¬ 
terior of shell mid-length; hinge width less than 
maximum width. Ventral valve evenly convex. 
Sulcus low, broadening anteriorly, arising close 
to umbo. Dorsal valve gently concave with low 
median fold often poorly developed. Interareas 
low, chilidium and pseudodeltidium poorly 
known. Ornament of capillae increasing by bi¬ 
furcation and intercalation. Growth lines fine, 
more pronounced anteriorly. 
Casts of worn ventral valves show external 
ornament poorly; those of worn dorsal valves 
show progressive absence of growth lines and 
presence of fine pseudocapillate ornament (5-6 
per mm at 6 mm from umbo) reflecting internal 
subsurface shell structure. Ventral hinge spines 
poorly known, appear to project at 40° to 45°. 
Ventral interior with distinct median septum, 
over half valve length at maturity, arising under 
ventral umbo. Parallel vascular trunks usually 
distinct adjacent to septum. Adductor scars in¬ 
distinct; diductors large, prominent, gently 
striated. Remainder of valve floor papillose. 
Teeth small, sharp. 
Cardinal process internally bilobate, exter¬ 
nally poorly known. Dorsal median septum dis¬ 
tinct, up to 0.6 times valve length. Ontogeny of 
dorsal septum reveals absence in juveniles, pres¬ 
ence well to the anterior of alveolus in sub¬ 
maturity but fused with lateral septa and an¬ 
terior of alveolus at maturity. Sockets distinct 
with pronounced inner socket ridges. Brachial 
ridges raised and papillose at maturity. Radi¬ 
ating rows of papillae in anterior of dorsal 
valve. 
Discussion. Neochonetes (Sommeriella) hockingi 
is distinguished from most other Western Aus¬ 
tralian representatives of the subgenus by its 
distinctive small size and low ventral sulcus. N. 
(S.) robustus Archbold, 1981 from the early 
Baigendzhinian Madeline Formation, Carnar¬ 
von Basin, is a slightly larger species with a 
distinctive rounded outline and is more con¬ 
cavo-convex than N. (S.) hockingi. The sulcus of 
N. (S.) robustus is virtually absent. The new 
species shares features with N. (S.) arabicus 
(Hudson & Sudbury, 1959) from the Sterlitama- 
kian to Aktastinian or younger Lusaba Lime¬ 
stone of Oman, an even smaller species with 
similar dorsal exterior and interior to those of A. 
(S.) hockingi. The Oman species is the smallest 
representative of Neochonetes (Sommeriella) 
known at present (Archbold & Burrett 1990). 
Order Productida Sarycheva & Sokolskaya 
1959 
Suborder Strophalosiidina Waterhouse 
1975 
Superfamily Strophalosiacea Schuchert, 
1913 
Family Strophalosiidae Schuchert, 1913 
Subfamily Strophalosiinae Schuchert, 1913 
Genus Strophalosia King, 1844 
Type species. Strophalosia gerardi King, 1846. 
Strophalosia jimbaensis Archbold, 1986 
Fig. 3A-P 
Strophalosia nov. sp.—Konecki et al. 1958:33. 
Strophalosia sp.—Condon 1963a: 11.—Condon 
1967: 114.—McGann 1976: 47, 
Fig. 3. A-P, Strophalosia jimbaensis Archbold. A. GSWA F43835, natural cast of dorsal exterior, x 1.3. B, GSWA 
F43836, natural cast of dorsal valve exterior, x 1.3. C, GSWA F43837, latex cast of ventral valve external mould, 
x 1.3. D, GSWA F43838, latex cast of ventral valve external mould, x 1.3. E, GSWA F43839, latex cast of ventral 
valve external mould, x 1.3. F, GSWA F43840, latex cast of ventral valve external mould, x 1.3. G, GSWA 
F43841, latex cast of ventral valve external mould, x 1.3. FI, GSWA F43842, internal mould of ventral valve, x 
1.3. I, GSWA F43844, latex cast of dorsal valve internal mould, x 1.3. J, GSWA F43843. latex mould from 
natural cast of dorsal valve interior, x 1.3. K, GSWA F43845, latex cast of dorsal valve internal mould, x 1.3. L. 
GSWA F43846. latex cast of dorsal valve internal mould, x 1.3. M. GSWA F43847, latex cast of dorsal valve 
internal mould, x 1.3. N, GSWA F43848, latex cast of dorsal valve internal mould, x 1.3.0, GSWA F43849. latex 
cast of dorsal valve internal mould, x 1.3. P, GSWA F43850, latex cast of dorsal valve internal mould, x 1.3. Q, 
R?, Aviculopecten sp., GSWA F43852, F43853, two small specimens, both incomplete, x 1. S, Fusisptrifer sp., 
GSWA F43851, incomplete internal mould of ventral valve, x 1. 
