202 MORIO. 



a number of small closely-set spiral lines intersected here and 

 there by obsolete growth-lines, and this in some individuals 

 persisted for at least one whorl. Gradually the longitudinal lines 

 develop into small ridges, which, after establishing small tubercles 

 ia the neanic stage, pass away into almost imperceptible striae 

 of growth. The tubercles on the shoulder of the whorl become 

 divided into two parts spirally at a very early period, and as 

 the animal arrived at maturity they are further subdivided in the 

 same direction. The spiral cords in the young shell develop 

 irregularly, but in the neanic stage they are transformed into 

 broad spiral ridges with concave sulci between. It is not until 

 the ephebic stage is reached that these ridges are crowned with 

 regularly spaced tubercles of similar character to those at the 

 shoulder of the whorl. It is interesting also to trace the develop- 

 ment of the broad area surrounding the suture. In the brephic 

 stage no indication of this is apparent, at least in any of tlie 

 specimens in the Museum ; but immediately afterwards an oblique 

 sulcus is gradually formed, which broadens and becomes flat 

 with age. 



It would not be difficult to trace the development of other 

 details of the ornament in the same way, but enough has been 

 said to show the absurdity of placing much reliance on the 

 character of the ornament in such a genus as Morio as a crileriou 

 for differentiating species, or even so-called "varieties." The 

 facts given suggest that if the growth of the shell in this and 

 some allied genera be studied in detail, it will be seen that 

 the difference observable in many so-called species are mere 

 individual characters, brought about by the suppression of bold 

 features, or the lack of accentuation in the adult of certain 

 characters which made their appearance at a much earlier stage. 

 lu judging the relative value of ornament in this connection, it 

 would seem that the most reliable differentiations are to be made 

 out in the younger stages of growth. Professor Tate is to be 

 congratulated in the moderation displayed in estimating the 

 number of species of Morio in the older Tertiary of Australia ; 

 contrast the work of Professor Sacco,' of Turin, in describing the 

 Cassidid^ of the Piedmont Tertiarv. 



1 Moll. Terz. Piedmoat e Liguria. Torino, 1890, p. 11 et sqq. 



