MACROSCHISMA. 189 



Genus MACROSCHISMA Swainson, 1840. 



Macrochisma SWAINS., Malacol., p. 356, 1840 ; type, M. hiatula 

 Sw., (Sowerby's Genera, Fissurella, fig. 5). Macroschisma of most 

 authors. 



Generic characters. 



Fissurellidce with an oblong shell not at all covered by the mantle, 

 and much shorter than the long fleshy foot, its apex near the posterior 

 margin, wholly removed by a large subtriangular fissure the wider end 

 of which is very close to the posterior end of the shell. 



The shell is situated on the front part of the body, the mantle ex- 

 tended a little in front of it. Tentacles long, subulate, the eyes on 

 slight swellings at their outer bases. Epipodial ridge wholly obsolete. 

 Anal tube rather long, directed backivard. 



Species distributed from Tasmania to Japan. 



The more obvious characters are the large fissure close to the 

 hinder end of the shell, margined inside by an entire narrow callus, 

 and the posterior position of the vertex. 



Swainson described Macroschisma as a subgenus of Fissurella. 

 The brothers Adams (Gen. Eec. Moll, i, p. 449) consider it a genus; 

 they commit the absurd error of mistaking the back for the front end 

 of the shell an error immediately detected by a glance at the 

 muscle impression inside. Gray, Sowerby, and even our model 

 systematist Fischer, all say that the perforation is close to the an- 

 terior end ! all of which goes to show how a book-maker depends up- 

 on his predecessors. 



Fischer, in classing Macroschisma under Fissurella as a subgenus, 

 is clearly in error. The group constitutes one of the most distinct 

 genera of Fissurellidce. 



Macroschisma has been monographed by Arthur Adams, Proc. 

 Zool. Soc. London, 1850, p. 202, (8 species) and by G. B. Sowerby 

 Jr. ; Thesaurus Conchyliorum, vol. iii, p. 205, (12 species). The last 

 monograph is valuable for its illustrations of Adam's unfigured 

 species, but none of the published descriptions are worth much. 

 Sowerby seems to have wrongly identified a number of forms (M. 

 hiatula Swains., for example), and for this reason I have omitted 

 referring to the Thesaurus in some cases. Thirteen species are de- 

 scribed herein, but some of them will doubtless prove synonyms. 



The animal pi. 59, fig. 59, of M. sinensis is thus described by Ar- 

 thur Adams : Animal very large and elongated, bearing the shell 



