BY JOHN MITCHELL. 547 



Gen. char. — Shell imperforate; umbo of pedicl* valve prominent, incurved, 

 depressed, and truncated by a circular foramen; cardinal area absent; hinge-line 

 straig-ht or nearly so; spiralia spiriferoid. Other internal structures not ob- 

 served. 



Genotype, Molongia elegans, n.sp. 



MoLONGiA ELEGANS H . sp . (Plate xxxi., figs. 6-8, 12.) 



Spec. char. — Valves strongly convex, the pedicle valve more so than the other. 

 Pedicle valve subrhomboidal, sulcus deep, smooth and wide, and on each side of 

 it are four radial ribs, all of which are prominent, except the one on each side 

 adjacent to the cardinal angles. Umbo prominent, incurved, truncated by a cir- 

 cular forapaen and resting on the umbo of the brachial valve, or nearly so. Brachial 

 , valve subquadrate, medial fold prominent and medially traversed by a narrow, 

 shallow sinus; the lateral folds agree in number and character with those of the 

 ventral valve, and alternate with them, thus giving to the lateral margins a zig- 

 zag outline: umVjo moderately prominent, and fills up the delthyrium. Hinge- 

 line straight, or almost so, and reaches to the cardinal angles which are nearly 

 rectangular in perfect and mature specimens. Hinge-line elevated. The whole 

 surface of the shell is traversed by faint, undulating, concentric growth-lines. 



Ohs. — This fossil in several respects is very spiriferoid. and in other features 

 it approaches forms of Trematospira. 



Loc. and horizon. — About eight miles west of Molong, Parish of Bomey, 

 County Wellington; Bowning, Parish of Bowning, County Harden. In both 

 localities it is a.ssociated with Atrjjponlea auatraUf; Mitchell and Dun. Appar- 

 ently Upper Silurian . 



Family RETZIIDAE. 



Retzia salteri Davidson. (Plate xxxi., figs. 4-5.) 



Terebratula salteri, Dav., Bull. Soc. Geol. France, 2nd ser.. vol. v., 1848, 

 p 331, PI. iii.. tig. 31; Bet~~ia salteri, Schmidt, Sil. Form. Ehsland, etc., 1858, 

 p. 212; Salter, Siluria, 2nd. edit., 1859, p. 250, Foss. 57, fig. 7; H. hai/lei, Lind- 

 strom, Gottlands Brachiop., Of vers. K. Vet.-Akad., Forhandl., 1860, p. 337; 

 K. salteri, de Koninck, Mem. Geol. Surv. N. S. Wales, Pal., No. 6, 1898, p. 27. 



Spec. char. — Shell e(|ually and strongly convex, oval ; valvjs almost of equal 

 size and each medially depressed. In the depressed part of the pedicle valve are 

 two less robust ribs than those on the lateral parts of the valve, and, in the corre- 

 sponding depression of the brachial valve, there is one such rib even less distinct 

 than those of the pedicle valve. On each side of these depressed ribs, in each 

 valve there are ten, simple and relatively strong ribs, making a total of twenty two 

 and twenty one on the pedicle and lirachial valves, respectively. The umbo of the 

 pedicle valve is only moderately prominent, incurved and apically truncated by 

 a foramen. The unibonal parts of each are strongly inflated. Hinge line short 

 and arcuate. Deltidial plates obscured. Margins practically non-sinuate. On 

 one side of our solitary specimen which is weathered the spiral lamellae are suffi- 

 ciently exposed to show that they possess the characteristics of the genus. The 

 concentric growth lines are fine, numerous and a.sperate. 



Dimensiom. — Length, 5.25, width, fi and depth, 3 lines respectively. These 

 measurements agree fairly closely with those given by Davidson for 7?. salteri 



