127 
Localities.—Streaky and Fowler Bays in the Great Australian 
Bight.* 
Eetorisma, gen. nov. 
Eiymology.—KEKctos, outside; ereisma, support; having refer- 
ence to the external ligament. 
Type.—Kctorisma granulata, spec. nov. 
Shell oval, thin, transparent, equivalve, inequilateral, slightly 
nacreous within ; valves gaping behind ; surface granulated. 
Right valve with a small cuneiform cardinal tooth. Left valve, 
with an obsolete socket beneath the umbo; the posterior and 
anterior margins of the hinge-line, where overlapped by the right 
valve, simulate ridge-like lateral teeth, the development on the 
posterior side being very pronounced, whilst it is somewhat 
obsolete anteriorly. Ligament external, supported in the anterior 
part by a linear-lanceolate extension of the hinge-line. 
Mantle open in front, mantle-margin without distinct sinus ; 
siphons united, very short, encircled with cirri ; foot conical. 
This genus by its external ligament, thin and granulated test, 
and its gaping valves, is closely allied to Pholadomya ; from 
Neeromya it differs by its dentition and closed valves. It has 
certain resemblances to Poromya, Cryptomya, and other related 
genera having an internal cartilage. 
Eetorisma granulata, sp. nov. Pl. i., figs. 3, 3a. 
Shell inequilateral, transversely oval-oblong, ventricose; anterior 
side rounded ; posterior side longer, with a narrowed subtrun- 
cated margin ; posterior margin slightly spreading to form a gape, 
2 mm. at the widest, and about 6 mm. in length. 
The umbos are large, transverse, approximate. Surface of 
valves ornamented with granules arranged in radial rows, the 
granulation is, however, more or less absent in the umbonal 
region, which is of a pearly lustre externally. There are 15 cirri 
surrounding the base of the united siphons. 
Dimensions.—Antero - posterior, 15; umbo-ventral, 11; sec- 
tional diameter, 7:5 millimetres. 
Locality.—Hardwicke Bay, Spencer Gulf ; two living specimens 
dredged from 8 to 10 fathoms by Dr. Verco. 
Genus MyseEua. 
Mr. E. A. Smith, in Annals and Mag. of Nat. Hist., 1891, p. 
235, suppresses this genus by including it under Tellimya, 
Brown (usually regarded as a section of Montacuta) ; and at the 
* Tasmanian examples have boen submitted to me by Rev. H. T. Hull, 
who considers it identical with Chemnitzia Beddomei, Petterd. 
