Growth stages in modern Trigonias. 21 



very variable in difterent individuals. It may be absent, 

 scarcely discernible, or well marked. In T. iutersitans the 

 character is much more advanced, though even here great 

 individual variation occurs. As regards the only other of our 

 species with discrepant ornament, T. tubulifera, I am unable to 

 speak in this respect. The species is small and closely beset 

 with tubular spines, so that the matrix is apt to adhere closely. 

 Pofessor Tate in his original description speaks of one specimen 

 in which the discrepant ornament was scarcely traceable, while 

 in another it was well marked. 



SUMMARY. 



The recent species, T. margaritacea, T. lamarckii, and the 

 miocene species, T. acuticostata and T. howitti, which are all 

 radially ribbed, show ancestral characters in the discrepant 

 ornament of the brephic stage. The older members of the group 

 Pectinatae, namely, T. subundulosa and T. intersitans, show, in 

 some individuals, a progress towards the ornamentation of the 

 more modern forms. The whole of the facts support the justice 

 of assembling all the species into the single group known as 

 Pectinatae. 



