INTRODUCTION. 13 



quadrate as in the Posidonomya and Iaoceramus ; and neither the wrinkles nor the ridges 

 (whichever may mark the valves of the Estheria) are bent off away from the umbo to follow 

 the outline of the produced ears of the shell present in most of the Aviculida, but absent in 

 Esther ia. Nor is there any trace of furrows or teeth on the hinge in Estheria. 



A general crumpling of the shell of a very thin Avicula or Posidonomya irregularly 

 corrugates the whole surface, concentric wrinkles and all ; but in Estheria the true 

 ridges are seldom thus interfered with, but rather yield to the transverse pressure by 

 taking on an obliquity of direction, leaving the sculptured interspaces to show the 

 crumpling effect of pressure. Rarely converted into calcareous matter, the Estherian 

 carapaces usually present a delicate, brownish, horn-like tissue, generally with some 

 degree of transparency and polish, contrasting with the dull perfectly calcified shells of 

 the Aviculida, or their bold wide-ridged impressions, black and filmy, or delicately 

 nacreous. In carbonaceous deposits the Estheria often leave only black films or merely 

 impressions. In one case a white siliceous (?) substance is found to replace the valves in 

 a brown-coal. Sometimes a ferruginous film has replaced the carapace-valves, especially 

 in sandstone. 



As the Estheria minuta has been referred to Posidonomya so generally and for so long a 

 time, it is highly probable that other little fossils of the same class still pass as Aviculida 

 in palseontographical works and collections. That attention might be turned to these, 

 I would point out some figured specimens which appear worthy of special microscopical 

 examination. The small shells figured by Pusch (' Polen's Palaeontolog./pl. 5, fig. 14) as 

 the young of Catillus Brongniarti have a strong resemblance to Estheria, and are the more 

 worthy of examination as they are said to come from the clay-beds above the Jurassic 

 limestone. Pigs. 11 and 12 of pi. 37 of Reuss's ' Kreideform. Bblim.' are not so 

 promising ; they may really belong to Tnoceramus Crisjrii and /. planus, to which they 

 are referred. Some of the fossils figured in pi. 17 of Lynch's ' Report on the Geology of 

 the Dead Sea ' might possibly be worth re-examination ; also the Australian fossil figured 

 in 'Annals Nat. Hist.' vol. xx, pi. 13, fig. 3. The Posidonomya Wengensis, Wissman, 

 and Avicula globulus, Wissm. 'Minister's Beitrage/ iv, p. 23, pi. 16, figs. 12 and 13, 

 from the St. Cassian beds of the Tyrol, should certainly be looked at by a crustaceologist. 

 Cardinianana, de Koninck, ' Anim. foss. Terr. Carb. Belg.' p. 71, pi. 1, fig. 6, is another 

 little shell to be examined. In the ' Geognostische Skizze der Umgegend von Ilmenau 

 am Thuringen Walde' (Zeitschr. deutsch. geol. Gesell. xii, 1860), Herr Karl von Pritsch 

 remarks (p. 144), " Near Goldlauter, not far from Ilmenau, some beds are nearly full of 

 C. nana. These flattened shells remind one of the Triassic Posidonomya minuta, Bronn. 

 Perhaps it is the same shell as von Gutbier mentions in his ' Versteinerung. des 

 Rothliegendes in Sachsen,' p. 7." 



