KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 52. wN:o I6. 15 
P. difformis n. sp. (Pl. 1, figs. 4, 5). Shell highly compressed, of a broadly 
ovate shape, truncated above by a straight extended hinge line. Anterior margin 
nearly perpendicular, with a slight sinuation above the middle, inferior one well 
rounded and posterior slightly curving. No distinct ears on the upper valve. 
Umbones triangularly projecting somewhat behind the middle of the hinge line, 
defined by a feeble radiating impression behind and a more distinct one in 
front. Inferior valve somewhat smaller and flatter than the upper one, with a 
deep byssal sinus, bounded by a straight anterior margin of the valve, with a few 
denticles above and an S-formed curvation of the lower margin of the wing. Sculpt- 
ure of both valves consisting of very fine radiating lines, more conspicuous towards 
the margins; the wing of the inferior valve with stronger radiating lire. Colour 
hyaline with radially stretched snowy dots spread all over. Maximal dimensions: 
height 10.2 mm; breadth (from anterior to posterior margin) 8.9 mm; thickness of 
the closed shell 1.9 mm. Locality: 45 miles W.8. W., 6 small sps with dried animals, 
attached to the basal part of a Turbinaria. 
Though certainly not full-grown, the largest of these specimens has such a 
peculiar form, aberrant from the normal shape of the Pectinidae, that it must be 
established as a new species. Above all the absence of ears is a remarkable charact- 
eristic. Compared with P. madreporarum Prrir, another speciessliving on corals, the 
new form is broader at the hinge line, is less oblique and far less tumid, and it 
has a different, much finer, sculpture. 
FAM. SPONDYLIDAE. 
Plicatula australis Lamarck. 42 miles W. 8S. W., 70 feet (#°/s), 2 sps, max. 1. 
28 mm; 45 miles W. S. W., 48—72 feet (°/;7), 4 sps, max. 1.35 mm. The specimens 
agree in their small red-brown dots all over the shell with fig. 10¢ in Renve, Conch. 
Icon. 19, 1873. It has been recorded from the Philippines and from Queensland 
(Lynee 1909, Hepiey 1910). 
FAM. AVICULIDAE. 
Pteria (Margaritifera) maxima JAmEson. 42 miles W. 8. W., 70 feet, 1 sp. 
(?°/s), 1. 33 mm; 45 miles W. 8S. W., 60—140 feet, many sps, max. 1. 70 mm (young). 
It was not until 1901 that this form, the largest mother-of-pearl oyster, was esta- 
blished, by JAMEson, as a distinct species. Previously it was included under P. mar- 
garttifera of Linn&. The distinctions between the two species were first pointed out 
by Savitte-Kent, though he thought the present form to be the typical P. mar- 
garitifera and named the second species Avicula cumingii Renve. JAMESON shows, 
however, that the present species is not identical with the Linnean type, from which 
it differs in being larger and flatter and having a longer hinge line, with which the 
posterior margin makes an acute or right angle. Further, the border of the nacre 
on the inside usually has a white or golden colour, whereas in P. margaritifera it is 
