Vol. 54.] MISS J. DONALD ON THE aENTJS ACLISINA. 45 



5. Observations on the Genus Aclisina, De Koninck, with De- 

 scEiPTioNS of British Species and of some other Carboniferous 

 Gasteropoda. By Miss .J. Donald. (Communicated by J. G. 

 GooDCHiLD, Esq., P.G.S. Read November 17th, 1897.) 



[Plates ILl-Y.] 



Introduction. 



In 1881 De Koninek, in hi-s ' Faune Calc. Carb. Belg.' Ann. Mus. 

 Boy. Hist. Nat. Belg. vol. vi, pt. iii, p. 86, created the genus Aclisina 

 to include some small shells which had previously been placed in one 

 or other of the genera Murchisonia, Looconema, Aclis, Turhonilla or 

 Turritella, and he thus defines it : ' Petite coquille allongee, conique, 

 a tours convexes, stries en spirale ; ouverture ovale ; bord externe 

 mince, entier et non saillant : columelle non arquee, legerement 

 epaissie ; axe non perfore.' 



Three species are described as belonging to this genus, but none 

 is especially regarded as the type. I have examined the shells 

 labelled as the types in the Brussels Museum, and find that they 

 are severally quite distinct from one another in character, so much 

 so, indeed, that each must form the type of a separate genus. It 

 remains, therefore, to be decided which should be regarded as most 

 typical of De Koninck's definition of Aclisina. The first-mentioned, 

 Murchisonia striatula, was referred by De Koninek in a former 

 work to the genus Murchisonia, '^ but he here removes it to Aclisina, 

 because he states there is no slit (' fente ') in the outer lip. 



The surface of the specimen from Vise in the Brussels Museum, 

 marked as the type of this species, is much worn, but it is suffi- 

 ciently preserved to prove its identity with other individuals from 

 the same locality in the Brussels Museum, in the Museum and in 

 the Collection of M. Destinez at Liege, and also with two shells 

 (65080) in the British Museum (Nat. Hist.). None of these 

 specimens agree exactly with either the figures or descriptions 

 of De Koninek. The whorls are less convex and the sutures are 

 not so oblique as in figs. 41 and 42, pi. xxxiii, vol. viii, pt. iv, but 

 the ornamentation is more like that of these figures than of figs. 57 

 and 58, pi. ix, vol. vi, pt. iii, where there is a band of four fine 

 threads near the middle of the whorl, while on the specimens I 

 have seen this band is formed of three rather strong threads, with 

 the exception of two individuals where the central thread is wanting. 

 As this part of the type is especially worn on the lower whorls, 

 the fine threads may have been inserted in the figure by the 

 artist if he had not a better preserved specimen to which to refer. 

 Yery few of De Koninck's figures are really portraits of the indi- 

 viduals marked as types which I have examined, but they appear 

 to have been generalized from several specimens, and they do not 



^ ' Descr. Anim. foss. Terr. Carb. Belgiqv.e,' 1842-44, p. 415. 



