Prof. T. Riqjert Jones — Fossil Estherice. 55 



called, which occurs with P. minnta in two specimens from the 

 depth of 612 feet in the bore-hole No. 3, near Diirrenberg, is long- 

 oval in shape; 1^"' long, and not quite V" high; convex; rather 

 smaller in front than behind ; ventral border convex ; the umbo 

 distinct and rounded. There are seven radials (three of them in 

 front, two in the middle, and one behind) reaching the border. An 

 eighth appears to follow the hinge-line backwards. About sixteen 

 regular, parallel, concentric lines cross the radials, and lose them- 

 selves in a series of roundish knots. The shell is very thin, of 

 a dark horn-colour, quite like that of the associated P. minuta. 



The relative size shown by Fig. 6 (about 2 mm., instead of 13 mm., 

 ■| inch), and the recognition of its alliance to and occurrence with 

 E. minuta, make it probable that the P. Wengensis of Giebel is an 

 Jistheria, and different from the P. Wengensis of Wissmann, as 

 intimated by von Alberti. 



1864:. Dr. F. von Alberti. Ueberblick iiber die Trias, etc., 1864. 

 (See also Geol. Mag. 1878. p. 102.) 



p. 192, note. — Posidonomya Wengensis, Giebel (not P. Wengensis, 

 "Wissmann, which is much larger), may be an Jistheria near 

 E. minuta, distinguished by Aveak radial lines. 



p. 193, note. — P. nodocostata, Giebel; from 192 m. depth in bore- 

 hole No. 3, near Diirrenberg; long-oval 0-003 m. long, and 

 0-002 m. high. Probably a crustacean. 



P. minuta is a crustacean ; so is probably Posidonia Albertii, Voltz, 

 probably the same as Posidonomya Germari, Beyrich [Zeitsch. D. 

 g. Ges. vol. ix. 1857, p. 377]. 



1875. E. Weiss. Zeitsch. D. g. Gesellsch. vol. xxvii. 1875, pp. 711, 

 712. 

 From the Lower Buntersandstein of Diirrenberg on the Saale, in 

 Saxony, some small shells are described as being in size and condi- 

 tion like Eslheria Germari of Beyrich, and occurring with it, but 

 differing from it by having a certain number of riblets radiating 

 from the umbo, aud thus constituting a new type. It is remarked 

 that Giebel had already described two species from Diirrenberg, 

 with the names of Posidonomya Wengensis and P. nodocost'ita, 

 which may perhaps be identical with the above mentioned. The 

 two latter came from a boring; but the foregoing were found in the 

 shales outcropping between the sandstone on the Saale, in the road 

 above the Salt-works of Herr Director Metzner, and the bore-hole. 

 When not well preserved, the valves lose their riblets near the umbo 

 and on the front and hind borders ; bnt these remain strongest and 

 most distinct in the ventral region. In good specimens these two 

 kinds of ribbing are readily recognized ; one kind consisting of about 

 12 riblets, of which the middle 6-10, very sharply defined and wide 

 apart, occur on the convex face, and are hollow on the inside of the 

 valve, as furrows, proportionally distant with smooth spaces between, 

 broken only by concentric wrinklings. This form may answer to 

 P. nodocostata, Giebel, which, however, seems to have only 7 riblets. 



