EEPORT ON THE GENUS ORBITOLITES. 9 



country whose range of study has been similarly wide ; ^ the doctrine that in each of the 

 two great series of Porcellanea and Vitrea " everything passes into everything else " 

 being one in which my friends W. K. Parker, T. Eupert Jones, and H. B. Brady entirely 

 accord with me. Not the less, however, do we all recognise the fact that particular 

 types of form are transmitted with marked genetic continuity, and the necessity, for 

 the purposes of systematic arrangement and description, of marking these types by 

 distinctive generic and specific names. 



The genus Orhitolites, as shall presently appear, furnishes a peculiarly illustrative 

 example of our mode of dealing with the subject. Four very well-marked types of form 

 present themselves, round which the entire assemblage of specimens collected over a very 

 wide geographical area, and from a great bathymetrical range, can be arranged without 

 difficulty. Three of them belong to the littoral zone of warmer seas, where (as on 

 the Fiji reef) they are generally found living together ; and they differ in little else than 

 grade of development, the smallest and simplest [Orhitolites margiiialis) retaining the 

 greatest resemblance to what may with almost certainty be regarded as the common 

 ancestral type of Orhitolites and Orhiculina; the next {Orhitolites duplex) being a transi- 

 tional form, in which the generalised ancestral characters very early give place to the 

 distinctive peculiarity of the Orbitoline type, while an indication is given of advance 

 towards the complexity of the highest and most specialised form ; and the third 

 {Orhitolites compilanata) being the one which shows all the peculiarities of the type 



' It is quite true that our conclusions on this point are not accepted by several Continental zoologists and palseon- 

 tologists of repute. Prof. Mobiua, for example, who a few years since brought home a gathering of Formninifera from 

 a reef off Mauritius, has expressed his dissent from it, on the ground that he sees no reason to believe that species are 

 less sharply defined among Foraminifera than they are in other groups of the Animal Kingdom, and that it is a logical 

 error to pass at once from the individual to the genus. Now I find in Prof. Mobius's own valuable monograph (Forami- 

 nifera von Mauritius) a very characteristic illustration of our position. The form he has described as Orhitolites com- 

 planata is so far from being a characteristic example of that species, that not only the central (or earlier) portion of the 

 animal figured by him (pi. iv., wrongly lettered iii., fig. 5), but the whole disk of which he gives a vertical section 

 (pi. V. fig. 2), save its three outer annuli, is formed upon the plan characteristic of my Orhitolites duplex, his specimen 

 being a young example of one of the transitional forms above adverted to. Now if Prof. Mbbius should reply that the 

 existence of such forms only shows that our conception of Foraminiferal species should be enlarged, and that the type 

 I have here distinguished as Orhitolites duplex should be merged in Orhitolites complanata, I have simply to reply that as 

 the two types are well and clearly differentiated in the hundreds of specimens of each which have passed under my 

 review, and as Orhitolites duplex is much more nearly allied in the " simplicity " of its structure to Orhitolites marginalis 

 than it is to the " complex " Orhitolites complanata, the utmost confusion would be the result of such an enlargement of 

 our conception of the latter, as would be necessary to enable it to include the former. If Prof. Mobius wUl attentively 

 study Part lii. of my Researches on the Foraminifera {Phil. Trans., 1859), he wUl find that, on the logical principle 

 he advocates, our conception of his Peneroplis pertusus must be enlarged to include not only all the species of the genus 

 Peneroplis, but also those of the genera Dendritina and Spirolina ; for my series of forms of these types, collected from 

 a very wide geographical area, and under very diversified conditions of climate and sea-depth, shows such a gradational 

 passage from one type to another, that it is impossible to break up the assemblage into even primary groups — much 

 less into secondary — that could be limited by precise definitions. I may add that before committing myself to the pub- 

 lication of an opinion which was at that time opposed to the doctrine taught by all the highest authorities in Systematic 

 Zoology, I had the advantage of submitting it to the criticism of M. Deshayes, one of the ablest Conchologists then 

 living ; who, after an attentive examination of the series which 1 placed before him, avowed his inability to draw 

 a definite line of demarcation through any part of it. And yet to abolish Peneroplis, Dendritina, and Spirolina as 

 " generic types " would be out of the question. 



(ZOOL. CHALL. EXP. — PART XXI. 1883.) X 2 



