Z ORCULA. 



Though the number of species is small, about 15, over 80 

 names have been applied to forms of one kind or another, 

 hence the length of this monograph. A large proportion of 

 the varietal names are not valid, being homonyms; but since 

 the taxonomic values are uncertain, the correction of nomen- 

 clature is left to European conchologists. 



The description of Orcula tingitana Pallary, Bull. Hist. 

 Nat. Afric. Nord, 1818, p. 149, is not accessible to me. 



Reinhardt (Jahrb. d. m. Ges., 1877, p. 280) has described 

 the lamellae of the early stages of 0. doliolum. A resume of 

 his description follows. 



The embryonic shell of 0. doliolum (pi. 5, fig. 1) has l 1 /^ 

 whorls and is smooth, but under high magnification it shows 

 close spiral striation on the upper side, which ceases abruptly 

 with the embryonic whorls, to give place to transverse ribs. 

 The lower side is smooth. Whether lamellas are present at 

 this stage was not ascertained, but none was seen through the 

 shell. In the following ribbed stage the ribs run out into 

 spines at the keel, as in A. aculeata, giving the young an ex- 

 tremely beautiful appearance ; they continue on the base and 

 gradually disappear towards the umbilicus. There is a sharp 

 thread median on the parietal wall, running far in and show- 

 ing through the shell. It usually appears as if interrupted, 

 with thickened white points, "knot-points", on the angles 

 (pi. 5, fig. 2). In one with 2 whorls, only the last half -whorl 

 ribbed, there are 2 knot-points. With the 3-whorled stage a 

 new thread, the columellar lamella, appears. There are there- 

 fore two threads, a parietal with 3 knot-points, and a sharp, 

 horizontal lamellar without knots (pi. 5, fig. 3). With fur- 

 ther growth the columellar lamella grows higher. The supra- 

 columellar appears weakly at the 41/o-whorl stage, and be- 

 comes distinct at 5 whorls. As the shell grows into the Pupa 

 form, the knots disappear. In the adult shell all of the 

 lamellas of the earlier whorls have disappeared. 



The presence of a lower-palatal fold, so far immersed that 

 it is subventral in position, was noticed by Bernhardt (1880) 

 but by no other author. Westerlund, indeed, doubted its 

 reality, thinking that what Reinhardt saw was the parietal 



