belonging to the Class Palliobranchiata. 



29 



Martinia, M'Coy 



Strigocephalus, Defr 

 Thecidea, Defr. .. 



Families. Genera. Characteristic Species. 



Spiriferidse ... A try pa, Dalm reticularis, desquamata, prunuin, 



{continued). tumida, concentrica, pectinifera, 



lamellosa, expansa, fimbriata, 

 planosulcata, Helmersenii, am- 

 bigua, ? Mantiae, ? serpentina, le- 

 pida, ferita, &c. 

 glabra, rostrata, Schl. not Zeiten ; 

 hyalina, lineata, laevigata, strigo- 

 cephaloides, pachyrhynchus, la- 

 bellum, &c. 

 Burtini, doisalis, &c. 

 Thecideidae ... Thecidea, Defr. ... Mediterranea, recurvirostris, ra- 



diata, hippocrepis, hieroglyphica, 

 &c. 



Respecting the generic arrangement adopted in the foregoing 

 table, it requires to be mentioned that I do not claim any consi- 

 deration for its being a natural one. My opinion is that no linear 

 arrangement can represent the true relationship pervading the 

 various genera of any class of animated nature. On this sub- 

 ject I have elsewhere offered my views*, and it is my intention 

 shortly to extend the same to a classification of the mollusks 

 under consideration. 



Atrypa, &c. 



Many palaeontologists are evidently unwilling to recognise the 

 genus Atrypa : Dalinan its founder, as is often done, included in 

 it some very different shells, as Atrypa reticularis, A. galeata and 

 A. nucella, inasmuch as the first is furnished with a pair of spiral 

 appendages t, the second possesses the internal structure peculiar 

 to the Pentameruses, and the third does not appear to be distin- 

 guishable from Hypothyris ; it therefore follows that the genus 

 requires to be considerably restricted. In this case we must not 

 overlook the species which Dalman first described, viz. Atrypa 

 reticularis, Linn., as we are compelled to consider it as the ty- 

 pical one. 



As its founder included a variety of forms in Atrypa, it is 

 to be expected that others would err in the same manner ; thus 

 J. De C. SowerbyJ includes in it the filose Spirifers of Phillips, 

 and such shells as Terebratula pugnus, Sow., &c, which belong to 

 other genera, the former generally to Oi'this and the latter to 

 Hypothyris. Mr. Sowerby has however been more fortunate with 

 such species as Spirifer eoopansus, Phill., and S. planosulcatus, 



* Vide Annals of Natural History, vol. xiv. pp. 271 and 272. 



\ Defrance was the first to make known the presence of these appendages 

 in Atrypa reticularis. (Vide Spirifer Sowcrbyi [= A. reticularis] in the 

 1 Dictionnaire des Sciences Naturelles,' tome 60.) I have a specimen from 

 the Eifel exhibiting the same appendages. 



% Mineral Conchology, No. 108. 



