1919.] E. W. Vredenburg : Shells of the family Doliidœ. 153 



tions of the genuine primary ribs. The intervals between the primary ribs are 

 decorated with subsidiary spiral threads. In the case of very small specimens, all 

 the wider intervals may contain a complete representation of intercalary threads 

 belonging to the second, third and fourth orders, the surface thereby acquiring a 

 remarkably elegant appearance. Anteriorly, as the intervals become narrower, the 

 intercalations may become reduced to the threads of the second and third orders, and 

 finally to a single intercalary thread, while sometimes the most anterior of all the 

 primary intervals, owing to its narrowness, is without any intercalation. These inter- 

 calary threads persist with increasing growth except those of the fourth order which 

 generally fade away. The ornamentation remains quite unaltered throughout a 

 wide range of successive stages of growth, but becomes somewhat altered in the 

 case of large, fully adult specimens, in which some of the intercalary threads broaden 

 out into flat bands resembling the primary ribs in shape, and filling a considerable 

 portion of the available interstitial space. Various inconsistencies are observed in the' 

 development of these bands : in most instances they are due to the broadening of 

 the median or principal intercalary thread, that is the thread of the second order, 

 which then forms a band separated on each side from the neighbouring original 

 primary ribs by a thin thread representing the original threads of the third order. 

 At other times the broadening affects not only the median thread of the second order 

 but also one of the flanking threads of the third order, and then the original primary 

 interval may contain two adventitious broad flat bands which may become quite 

 equal and may become shifted in such a way as to occupy a practically symmetrical 

 position within the original primary space. Lastly, there are instances in which the 

 broadening only affects one of the original, threads of the third order, and the result- 

 ing adventitious band is situated quite unsymmetrically with respect to the original 

 space. Threads of the fourth order are frequently revived on these adult specimens, 

 but their reappearance is very inconsistent. They are apt rapidly to assume the 

 same thickness as some of the threads of the second and third order, with which they 

 may form close-set groups of two or three spiral threads. Owing to this reappear- 

 ance of the threads of the fourth order, the most posterior primary interval (generally 

 the broadest interval) carries variously disposed groups of spiral threads of various 

 sizes, disposed differently in different specimens, the interpretation of which can only 

 be deciphered by following them (towards the apex along the spire. In a general 

 way, these adventitious ornaments of the full-grown shell are very variable, and no 

 two specimens are alike in this respect. They also commence to develop at various 

 sizes, but usually when the shell reaches or slightly exceeds a diameter of 60 milli- 

 metres. Nevertheless, in one specimen from Balasore Bay (M4408), measuring 120 x 

 96 mm., apparently the largest in the collection, the adult characters of the orna- 

 mentation have scarcely commenced to appear. The terminal zone of accretions is 

 posteriorly bordered by a narrow, feebly prominent, but sharp ridge, adjacent to 

 which the accretions to the actual notch form a rather broad band, almost flat in 

 some specimens, moderately convex in others, carrying crowded deeply concave lines 

 of growth together with a few distant obscure spiral markings. On the somewhat 



