BEACHIOPODA. 



115 



have been specially described in technical publications. 

 The British series includes the originals or type-specimens 

 of several species from the Lower Green sand of Up ware 

 described by Mr. J. F. Walker. Otherwise this portion of 

 the collection appears poor in type-specimens, owing to the 

 fact that so many are exhibited among the historical collec- 

 tions. Some attempt is therefore being made to show here 

 specimens interesting from their habit or structure. Such 

 are the examples of Spirifer, in which the arm-spires were 

 worked out with a needle and acid by the Eev. Norman 

 Glass, and specimens of Tcrehrcdula and Ornitliella from the 

 Cornbrash, showing the arm-loop. The interior of the shell 

 is also well shown in a Liotliyrina from the Norwich Chalk 

 on the other side of the Case. Another Jurassic brachiopod 

 Acantliothyris spinosa owes its name to the numerous spines 

 borne by its shell ; these were very long and are generally 

 broken off, but there are exhibited both British and foreign 

 examples in which they are most wonderfully preserved and 

 displayed. Productus is another genus richly provided with 

 spines, and these owing to their size are often found 

 scattered in the rock as thin tubes ; a slab of Carboniferous 

 Limestone covered with them is shown. A pretty impression 

 in flint of the rare Trigonosemus elegans is among the 

 Cretaceous fossils. Various Jurassic Terehratulse and tere- 

 bratuloid shells reflect changes of growth, due to old age or 

 illness, in variations of their ornament. The same outer 

 form has frequently been assumed by brachiopods of different 

 internal structure at widely separated geological periods, a 

 circumstance very perplexing to the field-geologist ; but here 

 is exhibited a set of four different species, belonging to at 

 least three genera, all coming from the Inferior Oolite Marl, 

 and so much alike that a casual observer could hardly tell 

 them apart. A similar independent recurrence of form is 

 displayed by Pygope and other " diphyoid " genera, in which 

 the fore-part of the shell has grown out into two lobes that 

 ultimately meet and enclose a vacant space. These various 

 modes of growth and of evolution are by no means confined 

 to Brachiopoda. 



Further information on the Brachiopoda may be sought 

 in the memoirs by T. Davidson already referred to, and in 

 "An Introduction to the Study of the Brachiopoda," by 

 J. Hall and J. M. Clarke (Albany, 1904-5). 



Gallery 

 VIII. 

 Table-ease 

 17. 



Table-case 

 18. 



Table-ease 

 17. 



Wall-ease 



llB. 



Table-ease 

 17. 



Wall-case 



llB. 



I 2 



