16 APPENDIX. 



Page 26, Terebratula. 



The Terebratula hitherto discovered in our British Jurassic beds may be arranged into two, or perhaps 

 three sections of that great genus, viz., Terebratula (proper), or those species provided with a short loop, 

 and of which Ter. maxillata, Sow. = (2 T . minor subrubra, Llhwyd, 1699), may serve as the fossil type. 



Secondly, into the section Waldheimia of King, which includes those Terebratulce possessed of a 

 lengthened loop, and more or less developed mesial septum in the dorsal or socket valve. W . orni- 

 thocephala and W. digona, Sow., sp., may be quoted as examples. 



Of the third section Terebratella, I am not positively certain that any species occur in the Oolites ; 

 T. hemispherica (Sow.) having been there located entirely on M. d'Orbigny's authority, as all my at- 

 tempts to discover the loop have proved unsuccessful from the want of a sufficient number of examples to 

 sacrifice to that object. It would be very desirable to ascertain whether this section be really represented in our 

 British Jurassic Fauna, and I trust the investigation will be continued on the first favorable opportunity. 



I fully admit having been greatly puzzled how to deal with many of the numberless varieties which 

 continually present themselves, in almost every species ; and have very probably now and then retained 

 under separate denominations forms which should have been united; but although I did not possess, at the 

 time, those connecting links which would have warranted such a union, I did attempt, in pp. 27 and 28, to 

 unite by a line several of those forms which seemed to me more closely allied, such as T. quadriflda and 

 T. cornuta ; T. resupinata and T. Moorei ; T. ornithocephala, T. lagenalis, and T. sublagenalis ; T. 

 punctata, T. subpunctata, and T. indentata ; T. perovalis and T. intermedia, &c. 



It has been subsequently found that some of these names may be advantageously expunged ; but the 

 question to exactly define what should be united and what separated, is not always so easy to establish as 

 many might imagine whose researches have been limited to a comparatively small number of individuals. 



In our retrospect view of the species published in this Monograph, we may begin by remarking that, 

 however nearly two forms may resemble each other externally, if the one possess a short loop and the 

 other an elongated one, they cannot be united, or considered as varieties of the same species, from zoological 

 considerations already detailed. Several questions having been repeatedly addressed to me, I will now 

 endeavour to answer them to the best of my ability. 



Page 28, Ter. quadrijida and Ter. cornuta 

 May belong to one single species, but i cannot add further details to those stated in p. 29. 



Page 36, T. numismalis, Lamarck, and var. subnumismalis. 



I am quite disposed to cancel my named variety ; but I should hesitate before admitting that 

 T. numismalis and T. quadrijida are varieties of a single species. 



Page 31, Ter. Waterhousii, Dav., 1851. 



M. Albert Oppel has recently described and figured what I take to be my species, under the new 

 appellation of T. subdigona. (' Mittl, Lias Schwabens Steitt.,' 1853, tab. iv, fig. 2.) 



Page 31, Ter. resupinata, Sow., 1812, and T. Moorei. 



The passages connecting the extremes of these two forms are so numerous, that it will be necessary to 

 consider the last simply as an inflated variety of T. resupinata, Sow. ; but I believe T. carinata of Lamarck 

 well distinguished by the shape of its beak and foramen. 



