186 Annals of the South African Muscitm. 



occurs which does not seem to express quite accurately the relations 



most frequently exhibited in the secondary ribbing. It is stated that, 



starting from the tubercles at the margin of the umbilical wall, there 



are groups of secondary ribs " which bifurcate higher up and admit 



of intercalary ribs." It would perhaps have been more correct to 



say that bifurcation of the secondary ribs on the flank (away from 



the tubercles) occurs rather as an exception than as a rule, since it 



is certainly either absent or very rare in the majority of known 



" Astieria." In typical specimens of H. astierianus (d'Orb.), as 



figured by d'Orbigny himself," no bifurcation in the costas of the 



rib-bundles after they leave the tubercles is apparent, but the finely 



ribbed forms (d'Orbigny's plate 28, fig. 4), which have been named 



H. sayni by Kilian and Astieria scissa by Baumberger, show the 



division of the ribs here and there on the flank. In all the South 



African representatives of Holcosteplianus the groups of secondary 



ribs proceed from the compressed umbilical tubercles and pass over 



the periphery to the tubercles of the other side without undergoing 



any division. It may be noted, however, that the ribs forming a 



group on one flank may become so disposed when traced to the 



opposite flank that they do not all reunite at one tubercle ; thus, of 



three ribs departing from a tubercle on one side, two may unite 



again at a tubercle on the opposite side of the whorl, while one may 



either pass to an adjacent tubercle or may terminate in the space 



between two tubercles at the umbilical rim. 



There is one other point in Uhlig's diagnosis of Astieria which 

 seems to call for emendation. It is stated that the ornamentation 

 " consists of a varying number of primary costee which start from the 

 suture, and at the passage from the umbilical wall into the sides 

 swell up into tubercles." A specimen obtained by Messrs. Eogers 

 and Schwarz near Uitenhage, and described below (H. uitenhagensis 

 sp. nov.), is so characterised that it can only be ranged among the 

 "Astieria" ; but in this example the ornamentation commences with 

 the marginal tubercles, and no primary umbilical costae are developed 

 in the last whorl. It seems therefore necessary to say that although 

 primary umbilical ribs are present in the majority of the Holcostepliani, 

 yet they do not form an essential part of the sculpture in all growth- 

 stages. It may be that in the specimen referred to, umbilical ribs 

 were developed in the earlier growth-stages represented by the inner 

 whorls, but these, owing to unfavourable preservation, unfortunately 

 cannot be studied. In this specimen, which is of considerable size, 

 the ultimate whorl probably represents a stage approaching, or in, 

 * d'Orbigny (1), p. 115, pi. 28, fig. 1 (1840). 



