180 RECORDS OF THE AUSTRALIAN MUSEUM. 



should be sufficient to separate them. I have seen no trace of an 

 external ligament in actual specimens of Stutchburia, but in one 

 of Morris' figuresf of S. costata, as it must now be called, there is 

 some shading above the hinge line that certainly does present the 

 appearance of a cartilage, but I think it is misleading and not 

 structural. 



Before proceeding with the specific descriptions, a few generic 

 points may be dwelt on more in detail. The dorsal or cardinal 

 margins, or liinge lines of the valves, are erect and unquestionably 

 closed, but on their inner and lower sides form thickened obtusely 

 rounded edges. These continue past thein conspicuous umbones, 

 and in their substance immediately anterior to the latter, are 

 excavated two depressions, one in each valve, which, in all prob- 

 ability gave attachment to the ligament at this end of the shell. 

 If not of this nature, the only other solution is that these depres- 

 sions are muscular. In the cast these thickened internal margins 

 are represented by wide, shallow, longitudinal concavities, whilst 

 thedepressions are indicated by two sharp projections about midway 

 between the umbones and the anterior adductor scars. The latter 

 are large and deep, in the type species at any rate, and must have 

 received strong and well developed muscles. On their posterior 

 sides the interiors of the valves were much thickened, and in con- 

 sequence deep depressions are left on the surface of casts, circum- 

 scribing the impressions of the muscles, which stand out boldly 

 from the general surface, with an oblique inclination to the anterior 



The posterior adductor scars are situated high up on the flanks 

 of the valves, immediately under the hinge lines, and although 

 conspicuous, are less so than the anterior. They have an oblique 

 inclination to the posterior, with the test correspondingly 

 thickened on their anterior sides, but to a smaller extent than 

 those of the other extremities of the shell. The simple pallial scars 

 are well defined, continuous, and from their prominence in casts 

 must have presented deep and sharp lines on the valve interiors. 



The following are the species known to me : 



Stutchburia costata, Morris, sp. 

 (PI. xxxi., fig. 1.) 



Orthonota ? costata, Morris, Strzelecki's Phys. Descrip. N.S. Wales, 



&c., 1845, p. 273, pi, 11, f. 1 (1 excl. f. 2). 

 Cardinia? costata, Dana, Wilkes' U. S. Explor. Exped., x., 1849, 



p. 692 (1 pi. 4, f. 8, 8a, 6, c). 

 Pleurophorus Morrisii, DeKoninck, Pal. Foss. Nouv.-Galles du 



Sud, 3. 1877, p. 143, pi. 20, f. 5. 

 Pleurophorus Morrisii, Eth. fil., Cat. Austr. Foss., 1878, p. 77. 



t Strezelecki.— Phys. Descrip. N. S. Wales, «&c., 1845, pi. 11, f. 1. 



