DAVIDSON — PAL^OXTOLOGICAL iS'OTES ON THE BRACHIOPODA, 101 



The following are the genera into which the families under descrip- 

 tion have been provisionally divided'"" : — 









Geological R 



ange. 



Family. 





Genera or Sub -genera, Author, Date, and 





c 



erous. 











a Typical Species. 





'5 





c 



6 











.2 



o 



> 



0 



1 















Q 



a 





H 



>-> 









X 















±1 J. Xa i_ O . J_/CtllXlt^Xl . XIJ^I . . * 



OT?Tin?5iTTJ A T)'Ovb 1 (*S4Q 



0. ciH07ncilu, 

 Streptorhynchus. King". 1850 



X 

 X 



? 



X 



X 



X 

 X 



X 







STROPHOMENID.E- 





S. pelargonafus. 

 Stkophomena. Rafinesqiie. 1S20 

 S. planumhona. 



X 



X 



X 













Leptjena. Dalman. 1827 . • . 



X 



X 



X 



'I 



X 



X 







S. tvcmsvevsalis. 



















Tropidoleptus. Hall. 1857 . . 



















T. carinatiis. 



















Strophodonta. Hall. 1852 . . 





X 











l 



S. depressa. 

















f 



Chonetes. Fischer. 1837 . . . 



X 



X 



X 



X 











C. sarcinulata, or C. Prattii. 

 Strophalosia. King. 1844 . . 





















X 



X 



X 







PRODUCTID^ . . 





»S'. Goldfussii. 

 AuiiOSTEGES. Helmersen. 1847 . 

 A . TV any enheimi. 









X 











Producta. Sowerby. 1814 . , 



? 



X 



X 



X 











P. gigantea. 















The generality of palaeontologists of the present day appear to be 

 agreed as to the propriety of forming two families out of the genera 

 or sub-genera above enumerated; but I am beginning to fear that 

 the characters by which some are distinguished will turn out to be of 

 less importance than was at one time imagined. 



It has been stated that external spines were peculiar to the Pro- 



Family names are derived from those in the typical genera ; and, as in the 

 present instance Sti-ophomena and Productus were established first, it behoves us 

 to admit them in preference to others subsequently introduced. Naturalists have 

 not hitherto agreed as to what should constitute a genus or sub-genus ; and as 

 some even entirely object to the term " sub-genus," I have not made any such dis- 

 tinctions in the table here given ; but I have endeavoured to arrange the names 

 according to their more probable affinities. When treating of the Strophomenidce, 

 we will endeavour careMly to compare the different "genera" or "sub-genera" 

 ■vvith each other ; as the differential characters do not appear to me to have been 

 in all cases satisfactorily established. 



