Reviews — J. M. Clarke — Protoconch of Orthoceras. 141 



these names for fossil genera, Mr. Whiteaves quotes the late Dr. 

 S. P. Woodward (Manual of the Mollusca, p. 414} that the molluscan 

 genera of the older rocks " are believed to be nearly all extinct, for 

 although the names of many recent forms appear in the catalogues 

 of Palseozoic fossils, it must be understood that they are only 

 employed in default of more exact information." Thus the Anodonta 

 Juhesii of Forbes, from the Upper Old Red Sandstone of Ireland, 

 is the type of the recently proposed genus Archanodonta ; and, 

 similarly, the species described as Unio by Sowerby, Phillips and 

 others, from the Coal-measures of Great Britain, are now referred 

 to Anthracosia or Ardhracomya. " But although there is at present 

 no satisfactory evidence of the existence of any of the recent 

 genera of Unionidse in rocks of PalEeozoic age, the family seems 

 to have been then represented by extinct genera, such as Amnigenia 

 (and possibly Archanodonta in the Devonian), by Naiadites or 

 Anihracomya in the Carboniferous, and by Falceomiitela and Palceo- 

 pleidon in the Permian." The specimens of Asthenodonta Westoni 

 (the subject of the paper) were found associated with large frag- 

 ments of Sigillaria and Lepidodendron, leaves of Cordaites, and a 

 piece of the lower jaw of a reptile. The stratigraphical position 

 of the sandstones in which the remains occurred is believed to be 

 between Coal Groups 31 and 32 of Sir J. W. Dawson's South 

 Joggins section, as described in the Accadian Geology. The external 

 contour of Asthenodonta Westoni is not unlike that of large specimens 

 of the freshwater pearl mussel (Margaritana margaritifera, Linn.), 

 but the beaks are more nearly terminal and the posterior termina- 

 tion of the valves more pointed below. The test is very thick, and 

 shows nacreous structure under the microscope. There are no traces 

 of lateral teeth in either valve, and the hinge dentition as a whole, 

 so far as it can be ascertained, is in some respects comparable with 

 that of Anthracosia. Until, however, the hinge dentition of both 

 of its valves is more perfectly known, the exact systematic position 

 of Asthenodonta will be uncertain; but it is considered by its 

 describer to represent an aberrant and extinct type of Uniouidas. 

 The length of the most perfect specimen collected was 200 mm. ; 

 height in the centre 90 mm. ; maximum breadth or thickness of 

 the two closed valves, about 42 mm. ; thickness of the anterior 

 end of the test of one valve, 9 mm. Akthuk H. Fookd. 



IV.— The Protoconch of Orthoceras. By J. M, Clarke. (The 

 American Geologist, Vol. XII. August, 1893, pp. 112-115.) 



THE fortunate discovery of a perfect specimen of the extreme 

 apex of an Orthoceras has enabled Mr. J. M. Clarke to supply 

 information, hitherto wanting, as to the nature of the protoconch 

 or initial chamber of that genus. Specimens showing the penul- 

 timate chamber, with external cicatrix, have long been known, both 

 frora the Carboniferous limestone of Belgium and from the Triassic 

 beds of St. Cassian. De Koninck has figured the Belgian examples 

 (Ann. Mus. Eoy. d'Hist. Nat. Belg.), Hyatt those of St. Cassian 



