OF CO^X'HOLOGY. 19 



NOTES ON THE GENERA ALARIA, DIARTHEMA, DICRO- 

 LOMA, &C. ; BEING A SUPPLEMENT TO "AN ATTEMPT 

 AT A REVISION OF THE STROMBIDiE AND APORR- 

 HAIDiE." 



BY W. M. GABB. 



In the last volume of the Journal of Conchology I published 

 a paper on the two families of alate shells, in ^Yhich I attempted 

 to arrange all of the genera as nearly in accordance with the 

 views entertained by students of the living forms, based on a 

 study of the animals, as our knowledge of their analogies would 

 permit. I pursued this course, not without some hesitation, 

 because, though the living representatives of both families are 

 sufficiently distinct, when we take up the paradoxical forms of the 

 secondary formations, and especially of the Jurassic rocks, we 

 encounter shells, the relations of which are almost impossible to 

 decide, if, as a basis, we start with the idea of two distinct 

 families. In view of this difficulty, several of the ablest students 

 have preferred to cla-ss them together. Pictet (Paleontologie 

 Suisse, 1860), calls them all Stromhidoi, while, more recently, 

 Stoliczka (Pal. Indica, 18G7,) proposes the new term Alata, a 

 name very appropriate in its etymology, but not admissible, 

 inasmuch as it has not the termination required by custom for 

 all family names. If we permit these close resemblances to guide 

 us, it is difficult to say where we will stop. Grant that the two 

 families should be consolidated ; the next question that arises is, 

 where are we to draw the line between the family thus consti- 

 tuted, and the Ceritlddce ? The analogies between Aporrhais 

 and CeritMum in the animals have been long known, and is there 

 not strong ground for supposing that Piette's Eustoma should 

 serve as the connecting link ? Or further, on the other hand, 

 should not Alaria, JJiarthema and Spinigera unite them with 

 Ranella f 



A parallel case of two very distinct modern families becoming 

 confused and apparently blending, as Ave go back in the geolo- 

 gical scale, occurs in the Aviculidce and Pectenidce. No one 



