203 



foramen when adult. It is evident from the mode in which the slit 

 is finally closed by the lateral expansion and union of its edges, 

 that this change is final, and coincident with the termination of the 

 shell's growth ; whereas in the extinct Trochotoma the foramen 

 must have been established at an early period, and continued to 

 travel onward with the growth of the shell, as in the genus Rimula. 



Eleven species of Scissurella are enumerated by Messrs. H. and A. 

 Adams, under the generic name " Anatomus " * :— - 



angulatus, Sow. d'orbignyi, Audouin. 



asper, Phil. indicus, Montf. 



bertheloti, Webb. Icevigatus, d'Orb. 



conicus, d'Orb. striatulus, PhiL 



costatus, d'Orb. reticularis, Phil. 



crispatus, Flem. 



Of these, A. costatus and A. Icevigatus are only varieties of A. 

 elegans ; " reticulatus " appears to be a misprint for S.plicata, Phil., 

 of which S. d'orbignyi, Scac. (not Audouin), is a synonym ; and both 

 this and S. striatula are only varieties of S. elegans, d'Orb. S. 

 angulata, Loven (not Sow.), appears to be the adult Norwegian form 

 of the British S. crispata ; and S. asper a } Phil, (described as fossil 

 only), is the Mediterranean equivalent of the same species. 



Instead of eight or nine European species of Scissurella, I can find 

 only two ; and of these the typical species must be called S. elegans 

 (d'Orb.), that being the only appropriate name of the three first 

 given. 



S. bertheloti, Webb, from the Canaries, is closely allied to S. ele- 

 gans ; S. conica, d'Orb., from the Falkland Islands, is more like 

 S. crispata. The British species, S. crispata, differs considerably 

 from the typical Scissurella in form ; and the slit is permanently open, 

 as in Pleurotomaria, — a character which may be considered of sub- 

 generic importance. Prof. King, in his otherwise excellent remarks 

 on this genus (Pleurotomaria), assumes its identity with Scissu- 

 rella (crispata), and supposes it to be " essentially non-perla- 

 ceous | ; " but since the Cretaceous, Tertiary, and recent species 

 of Pleurotomaria are all nacreous, it is reasonable to conclude that 

 those of the older rocks were likewise so, although now metamorphic 

 and destitute of any remains of pearly lustre. Scissurella of 

 d'Orbigny, typified by S. elegans, is distinct from every other genus, 

 recent or fossil, hitherto described. 



The Messrs. Adams have substituted for Scissurella the name 

 " Anatomus, Montf.," which certainly was never intended for any 

 shell of the kind. Montfort's figure was most likely taken from a 

 specimen of Serpula spirorbis, which agrees with the description of 

 "Anatomus indicus " in being gregarious upon sea-weed, and in 

 having, when detached, a slit in the lower margin of the lip. 



If it should still be considered desirable to have a subgeneric 



* < Genera of Shells,' p. 439 (June 1854). 



f Monograph of Permian Fossils, Trans. Pal. Soc. 1850, p. 215, 



