LITHODOMUS LINGUALIS. 77 



hinge-line, bufc no specimens whicli have come into my hands have the dorso- 

 ventral measurement anteriorly equal to that in his fig. 2, unless they have been 

 flattened and expanded by crushing. 



In the measurements given Mr. R. Etheridge, jun., uses the term length for 

 dorso- ventral, and width for antero-jjosterior diameter. 



This author refers to Llthopliaga ? lingualis, of Meek and Worthen (op. 

 cit.), from the Keokuk group of the sub-Carboniferous series of Illinois and 

 Indiana, as apparently resembling his shell very closely. These authors state, 

 " We are by no means satisfied that this is the species described by Phillips, but 

 prefer to refer it provisionally to that species, rather because we have been 

 unable to find any very reliable differences, than from any great confidence in its 

 exact identity." They note that many of their specimens are much larger than 

 the one figured by Phillips. Judging from the figure given, I should think the 

 reference of the American specimens to L. lingualis correct. 



A very fine series of shells, forty-five in number, named Modiola fusiformis, are 

 in the collection made by de Koninck, now in the Musee de I'Histoire Naturelle 

 of Brussels ; several of them are figured in his great work (op. cit.). There is 

 a large amount of variation to be noticed in this series, the depth of the 

 posterior end and the comparative extent of the hinge-line differing slightly in 

 many of them. I have little or no doubt that these shells are identical with those 

 named M. lingualis and M. lithodomoides from British rocks, and have therefore 

 placed M. fusiformis, de Koninck, as a synonym of Phillips's species. I have no 

 hesitation also in referring M. princeps, de Koninck, to the same species. 

 M. Fraipont, who is responsible for the sections on Modiola, says in his remarks 

 on this fine shell, " Cette magnifique esp^ce s'eloigne de la plupart de ses 

 congeneres et surtout de la M. lithodomoides, R. Etheridge, par ses proportions 

 et par sa forme generale." The description would do very well for the British 

 shell, with the exception that it is stated " bord ventral droit," notwithstanding 

 that the figure shows a ventral border concave in its middle third. The approach 

 to angulation of the posterior border is neither described nor depicted, but the 

 type specimen shows this character very plainly marked. In fact, M. princeps 

 differs from the adult form of M. lingualis in no characters of specific value, 

 mere size in a single example being no sufficient indication for the creation of a 

 new species. There are, however, three smaller specimens mounted on the same 

 plaque as the figured specimen, also named M. princeps^ which are no bigger than 

 the ordinary adult British forms. 



The form M. Cordolianus, de Ryckholt, approaches very closely to the species 

 under description. It appears that only the type and one other specimen are in 

 the de Koninck Collection. The former is more expanded posteriorly and flatter 

 than in specimens of the same size of L. lingualis, but this may be due to the fact 



