DR. T. DAVIDSON OX RECENT BRACHIOPODA. 5 



lu his second group he unites those forms in which the brachial apparatus or loop 

 undergoes numerous transformations from the embryo up to the adult condition, and 

 which have been distinguished by the names of Platydiform, Magadiform, and Megerli 

 form stages. The mantle in this group is not provided with those calcareous spicuhi 

 which occur so constantly in the first grovip. The colour also of the dried animal is 

 yellowish, whilst in the first group the hue or tint of the dried arms and of the peri- 

 pheric portions of the mantle are of a very clxaracteristic dim white. This, I may, 

 however, remark, is not always the case, as I possess specimens of the dried animal of 

 several species of TerebratuUna that are of a decided yellow colour. The group would, 

 according to M. Deslongchamps, comprise the recent genera Waldheimia, Macandrevia, 

 TerebrateUa, Laqueus, and Magasella. 



While fully appreciating the importance of all characters derived from a study of the 

 animal, I am not convinced that the temporary modifications in the shape of the loop, 

 or tlie presence or absence of calcareous spicula in the mantle, &c., are indications of 

 sufScient importance or permanence to supersede those derived from the adult shape of 

 the calcareous lamellae supporting the labial appendages, — characters which are often 

 accessible, and of important assistance in distinguishing the moi*e numerous fossil 

 members of the group. Moreover, Mr. W. H. Dall, in describing the animal of Wald- 

 heimia floridana (Bull. Mus. Comp. Zool. Harvard, vol. iii. p. 16, 1871), distinctlv notes 

 the existence of a few exceedingly delicate spicula in the floor of the great sinuses. It 

 would seem therefore that these spicula occur in a genus which M. E. E. Deslongchamps, 

 in his proposed new classification of the Terebratulidae, places among those forms charac- 

 terized by the entire absence of spicula. 



After long and searching examinations of the recent forms, I have described in this 

 monograph about one hundred so-termed species, some varieties, and about twenty- 

 eight uncertain ones. Of course the vexed question as to what really constitutes a 

 species remains the same, and is likely to remain so for a long time to come. 



It will not be necessary to extend these introductory remarks, as all details have been 

 fully given under each species. In conclusion I would tender my grateful thanks to the 

 many kind friends who have in so zealous a manner supplied me \\\t\\ valuable infor- 

 mation and specimens *. 



AETIIROPOMATA, 0\veu=CLISTENTERATA, King. 

 Family TEREBRATULID^, (Gray) emend. Davidson. 



Subfamily Tbrebkatulin^, Dall, 1870. 



During the last few years a strong desire has been manifested by those palaeontologists 

 who consider an extreme subdivision of genera desirable, to separate from Terehratnla 

 proper those forms characterized by a small short loop, of which the principal stems are 

 united anteriorly by a slightly arched lamella, and of which Liothyris vitrea may bi- 

 taken as the type. 



* The drawings for tho Plates were made by myself, on paper: but the state of my health would not allow of my 

 reproducing them on stone. 



