part 3] THE THiAS or xew zealaxd. 199 



Halobia hochstetteei Mojsisovics. (PL XXI, fig. 3.) 



1874. ' Ueber die Triadischen Pelecypodengattungen Daonella & Ualohia ' p. 32. 

 & pi. iii, ligs. 7-9. 



Hinge-line straight, the heak directed forwards, not very pro- 

 minent, and situated rather in front of the median line. The 

 anterior ear is triangular in shape and Avidens rapidh'-, is not inflated 

 or rounded, and is marked off from the rest of the shell by a narrow 

 and somewhat angular sulcus. The primary radial ribs begin 

 below the beak, and consist of a series of rather broad flattened 

 ribs of irregular width, separated by well-marked and rather deepl}^ 

 cut grooves. On these ribs two or three very much fainter secondary 

 grooves occur some distance from the beak. At some distance 

 below the beak (the distance seems to vary in different specimens),, 

 the ribs become Avavy and bend very strongly forwards, continue 

 thus for a short space, and then curve gently downwards again 

 towards the lower and anterior margin. The hinder portion of 

 the shell below the hinge-margin is devoid of ribs and almost 

 smooth, and the ribs become very feeble towards the lower posterior 

 margin in fully-grown shells. The anterior ear bears a shallow 

 radial furrow not far below the hinge-margin. 



Broad concentric growth-ripples occur on the young shell, but 

 they are faint and rather irregular, and they tend to occur also on 

 the anterior ear. Since specimens of any size are almost invariably 

 broken, I cannot describe the marginal outline with any certainty, 

 but it seems to have been similar to that of H. ziUeli var. 

 zealandica. This shell also attains a large size : for instance, 

 a fragmentary specimen in my collection must have been 65 mm. 

 long and 40 mm. high. 



Locality and horizon. — Crest and saddle of Mount Hesling- 

 ton. Nelson. Bed e, Otamita, Hokonui Hills. It occurs in the 

 same bed as the last-described form, and I collected several 

 specimens of it. 



Remarks. — Mojsisovics figures three specimens of H. liocli- 

 sfetferi, all of small size, which were apparently brought to Europe 

 by Hochstetter and had been identified by Zittel as Ualohia 

 lommeliy Mojsisovics gives a long and clear description of this 

 form, of which the following are the main points : — 



It is a rather high form, iinstriated towards the hinder hinge-margin, with 

 a -wide anterior ear, on which beneath the margin a rather strongly-arched fold 

 occurs, split at some distance from the beak by a sunken groove. Primary 

 radial grooves are not numerous, and the ribs that they form are divided at 

 varying distances, by further single or double g-rooves, into secondary ribs of 

 dissimilar width. Near the forward and hinder part smaller ribs occur. 

 Anteriorly the ribs reach to the ear. The ribs do not run straight, but imdergo 

 several bendings to and fro similarly, as is generally the case in the group of 

 m. fallax. The wavy breaking of the ribs does not take place in all examples 

 at the same age, and he remarks that it would be interesting to know 

 whether this corresponds to any difference in geological age. Concentric 

 ripples are very apparent on the upper half of the shell. Length = 13 mm.; 

 height =10 mm. 



^ Bibliography, 51. p. 27 & pi. vi, figs. 2 a-2c. 



It 2 



