Manchester Memoirs, Vol. Iv. {\^\i), No. W,. 5 



The pustules in one type {T. Danioniana a) are small. 

 In T. Damoniana |3 they are large. 



The typical T.gibbosa of Lycett has reached a slightly 

 further stage in the development of ornament than 

 T. Damoniana o. Its carinal space is larger and better 

 defined, and its costations are further broken up. Some 

 Gibbos?e of Lycett exhibit total loss of costations, and 

 some total loss of ornament. These may be counted as 

 T. gibbosa /3 and 7, or possibly as gerontic stages of 

 T. gibbosa a. The pustulations of T. gibbosa are larger 

 than those of 7". Damonia)ia a. 



The ontogeny of T. gibbosa is excellently shown by 

 young and adult specimens from a block of Portland 

 stone in the Manchester Museum. Here the youngest 

 shows a pure RL cnrvirostris type, the next a T. costatula 

 stage and a later stage giving the introduction of an 

 undulate type. These stages are again reproduced in 

 well-preserved adults from the same block. {Figs. IV. to 

 VIII. of Plate) 



T. Damoniana (5, as figured by Lycett in his mono- 

 graph, appears to correspond with T. gibbosa j3, that is 

 to say, its ephebic ornament is purely tubercular, the 

 T. gibbosa a and T. Davioniana a types being lost after 

 neanic stages. (Fig. IX. of Plate.) 



T. tenuitexta appears to be a further stage of T. Da- 

 nioniana a, as its tuberculations are small, and further 

 developed than in that form. 



This typeof umbonal marking is seen in the Cretaceous 

 of India and South Africa in the forms described by 

 Dr. Kitchin. Here, however, the flank markings are 

 further modified by their junction into a V which, much 

 as in Gonioniya, occupies the whole flank. 



