OF CONCHOLOGY. O 



the other, and obliquely truncated ; dorsal margin sloping 

 in front of the beaks, and more nearly horizontal and appa- 

 rently without an escutcheon behind them ; ligament external 

 or marginal, rather long. Surface with concentric lines and 

 ridges, and sometimes obscure radiating markings on the umbo- 

 nal region. (Hinge muscular, and pallial impressions unknown.) 



Type. Promacrus nasutus, M. 



Although this group is here proposed as a subgenus under San- 

 guinolites, I have thought it desirable to give its characters in 

 rather more detail than is usual in defining a subgenus, because 

 it is really very doubtful whether these shells can be properly in- 

 cluded, even as a marked subgenus, under that group. Until 

 the typical species of Prof. McCov's genus can be better known, 

 however, I have concluded to place them under that genus, with 

 a distinct name that can be retained in a generic sense, should 

 these shells be found to belong to a new genus, as they most 

 probably will. They certainly differ from any of the species 

 included in Sanguinolites by Prof. McCoy, as well as from his 

 diagnosis, in having the anterior side much produced and atten- 

 uated, instead of " short, rounded," and in having the margins 

 closed all around instead of "gaping" behind. In re-defining 

 his genus (British Paleozoic Fossils, p. 276) Prof. McCoy also 

 distinctly states that its hinge margin is " inflected to form a 

 long posterior lunette ;" while in the shells here under conside- 

 ration it seems to be erect, with ^he long ligament rather deeply 

 inserted between the erect edges. 



With due deference to the acknowledged ability of that dis- 

 tinguished palaeontologist, it certainly seems to me that Prof. 

 McCoy has included in Sanguinolites, as I have elsewhere inti- 

 mated (Palteont. Upp. Mo. p. 39), forms belonging to more than 

 one genus. Some of these appear to be identical with AUorisma, 

 King, but as it remains to be seen whether or not Prof. McCoy's 

 typical species (Sanguinaria angustata, Phillips) really possesses 

 the characters of AUorisma, I am not yet prepared to agree 

 with those who regard the latter group as being synonymous 

 with Sanguinolites. 



* It is very much to be desired that some one having access to the 

 better specimens of British Palaeozoic Lamellibranchs, doubtless now 

 known, than those originally described by Phillips, Sowerby and others, 

 should give full descriptions and illustrations of these shells, as Mr. Da- 

 vidson has done of the Brachiopoda. This is all the more necessary, be- 

 cause later authors have either expressly cited some of these species as 

 types of their new genera, or so alluded to them that they will probably 

 have to be regarded as the types of the same, and yet these typical forms 

 must remain very imperfectly known to all who have not access to au- 

 thentic specimens, until better illustrations and descriptions of them have 

 been published. 



