APPENDIX. 245 



disposed to consider, that similarity of apopliysary systems constitutes a stronger bond of generic affinity 

 than similarity of external characters ; and in this respect, I believe, that I am fortified by the opinion of 

 Mr. Davidson, whose knowledge of the interiors of Ancylobrachial genera is of the highest order. 



Now, as the first-described genus of the singly-attached-looped Ancylobrachial group is Terebratula, it 

 will be necessary, in considering this group as a family, to name it Terebratulidcs ; and, on the other hand, 

 as the original genus of the doubly-attached-looped Ancylobrachials is Terebratella, we are also compelled 

 to consider these, as constituting the family Terehratellidce. These two families may, therefore, be con- 

 stituted as follows : 



Terebratulidce. Terebratellidce, 



(Genera with a singly-attached loop.) (Genera with a doubly-attached loop.) 



Terebratula. Terebratella. 



Terebratulina. Megerlia. 



Belthyridcea (?) Ismenia. 



Waldheimia. 

 Epithyris, 

 Pygope. 



It requires to be observed, that I now entertain very little opinion of any of the above genera being 

 without an apophysary system : if this be correct, Rhynchora will have to be stationed in either one or 

 the other of the above families. The family Rkynchoridcs, if its type have a doubly-attached loop, will have 

 to bear this name instead of that of " Terebratellidce ;" but until this is settled, it seems preferable to make 

 use of the latter name. 



Strophalosia Morrisiana, p. 99. 



An oversight was made when describing this species. Nothing was then stated of the lower or small 

 valve being furnished with spines. Figure 26, in Plate xii, represents a gutta percha cast of an impression 

 of this valve, found in Whitley Quarry, which shows that the spines are not so numerous as those of 

 Strophalosia excavata, nor so regularly arranged. 



Spiriferidce (Apophysary system of), p. 122. 



In noticing the cross-piece which Mr. Davidson has discovered connecting the two spirals of some of the 

 Jurassic forms of this family, I made the suggestion, that it had resulted from the approximation or union of 

 the two crural processes. This view is strongly supported by what is seen in the loop of Terebratulina 

 caput-serpentis, as-will be shown hereafter. 



Ismenia, pp. 142-145. 



Through an error, I typified this genus with Schlotheim's Terebratulites pectunculus, instead of his 

 Terebratulites pectunculoides. I am enabled, by the beautiful figure which Mr. Davidson has lately 

 published of the latter species (Fide Annals and Mag. of Nat. Hist., 2d series, vol. v, plate xv, fig. 5), 

 to add to the diagnosis of this genus the following character of its apophysary system : Loop elongated ; 

 deeply recurved ; armed at the recurving bend with several cilia-like processes ; and attached anteriorly to a 

 long medio-longitudinal plate. 



