Dr. W. B. Carpenter on the Polytremata. 385 



into a tube) communicating with each principal chamber of 

 the successive whorls ; and thus the specially Globigerine type 

 is maintained throughout. As the successive chambers en- 

 large, a tendency shows itself to subdivision into chamberlets 

 by a thickening or infolding of their outer wall ; but although 

 this partial subdivision gives to the external surface an areola- 

 tion closely resembling that of Polytrema^ the resemblance is 

 for the most part apparent only, the subdivision seldom going 

 so far as to cut off these chamberlets from the general cavity 

 of the chamber. The two types thus differ essentially, not 

 merely in plan of growth, but in the relation of their small to 

 their large cavities ; for while the branching canals or utri- 

 cular dilatations of Polytrema are mere cavitary interspaces in 

 the midst of a fabric built up by the aggregation of minute 

 chambers, the cavities of Garpenteria are its true cJiamhers 

 arranged in regular spiral succession, and are separated from 

 each other by complete septa, whilst partially subdivided into 

 chamberlets by imperfect septa. Hence, however strong the 

 general resemblance between Mr. Carter's Polytrema utricidare 

 and his P. halaniforme ( = Garpenteria)^ I hold that their 

 morphological difference is quite sufficient to justify the reten- 

 tion of Garpenteria as a distinct generic type — its alliance 

 being rather with Glohigerina than with Polytrema^ and the 

 latter, like Tinoporus^ being an extraordinary development of 

 the Planorbuline type. 



If Mr. Carter can show that fundamental differences of 

 similar importance exist between Patellina and Gonulites^ I 

 shall willingly accept his plea for the retention of the latter 

 genus, which I only merged in Patellina because it seemed 

 to me (as to my coadjutors, T. Rupert Jones and W. K. 

 Parker) to agree with that type in plan of growth, and to 

 differ from it only in degree of development. 



Both tliese opinions I hold (as I hope that I do all others) 

 with a readiness to modify or surrender them as further 

 extension of our knowledge in regard to the subjects of them 

 may require. And in this connexion it gives me great plea- 

 sure to be permitted by my friend Mr. Carter to cite the follow- 

 ing passage relative to my ' Introduction ' from a letter he 

 has been good enough to write to me on the questions under 

 discussion : — 



" Of course you feel interested in what you yourself have 

 indicated in your ^ Introduction ' on Polytrema and Garpen- 

 teria ; but the title itself of your work means no more ; and 

 as in natural science all is progressive, and as much due (and 

 even often more) to those who have introduced a subject, as to 

 those who have made the introduction a stepping-stone to 



Ann. & Mag. N. Hist. Ser. 4. Vol. xvii. 26 



