343 



TEREBRATULIDiE. 



The genus Terehratula of Brugi^re — the original Ano- 

 mia, although the latter name has been appropriated, as 

 we have seen, by a very different assemblage of shell-fish — 

 included within itself those shells which present a general 

 similarity of form, due to the inequality of their valves 

 and the perforation on or under the beak of the upper 

 and larger valve for the passage of a muscular peduncle 

 by means of which the animal is fixed to rocks^ or shells, 

 or other extraneous bodies. Most writers on existing 

 shells use the term Terehratula in the Brugierian sense, 

 but palaeontologists have become more and more im- 

 pressed with the necessity of breaking up this really vast 

 assemblage of species, not merely on account of their 

 number, which would be but a sorry reason for generic 

 dismemberments, but because included in it we find lesser 

 groups exhibiting important characters of structure, evi- 

 dently of high value, whether we consider the features 

 of the shell or the arrangements of the soft parts within 

 it. As these subdivisions of the old genus Terehratula 

 appear to have a value fully equal to the generic sepa- 

 rations which we have admitted among the Lamellihran- 

 chiata, we feel bound to adopt them, however much our 

 doing so may seem an innovation on conchological practice. 



Baron Von Buch, one of the most philosophical of living 

 palaeontologists and geologists, was the first clearly to see 



