﻿SONNININ^E. 



315 



This can hardly be an adult form. It is, presumably, only a youthful form of 

 an unknown adult, but it is certainly the earliest, biologically, of the series ; and 

 it may be considered as the " morphological representation "* of an earlier adult 

 of the phylogenetic series, in accordance with the law of earlier inheritance. 



In the same way earlier inner whorls of Sonn. multispinata, so far as they can 

 be seen, are a morphological representation of a still earlier ancestor of the genus ; 

 and this is confirmed by the inner whorls of other species. 3 Such an ancestor 

 would be evolute, slowly-coiled, with a broad sulcate-carinate abdomen almost 

 flat from spine to spine, and the spines themselves in a regular sequence. Sonn. 

 multispinata shows the commencement of the change which produced a more 

 gibbous and narrower abdomen. 



Roughly speaking, with the exception of this species, all the Sonniniss known 

 are examples of retrogression 3 from the type of which Sonn. multispinata is the 

 morphological representation ; although there is, as it were, a certain want of 

 decision about the retrogression of the earlier species. In fact, although there 

 are many species* of the genus which are extremely retrograde forms, yet the 



1 It becomes absolutely necessary to employ a phrase of this kind in a definite manner in 

 connection with the phenomena of earlier inheritance. In tracing a genetic series upwards the adult 

 stage of an early species, say a, becomes adolescent in the later form, b, infantile in c, and so on. 

 Therefore I wish to call the adolescent B the " morphological representation " of the adult a, and the 

 infantile c the "morphological representation" of adolescent b or of adult a. In the same way 

 adolescent c is the " morphological representation " of adult b. In reverse manner adult a may be 

 spoken of as the " morphological prefiguration " of adolescent b, or of infantile c, and so on. We 

 thus obtain, with a phrase of Hyatt's, three terms in regard to the relations of an individual. It 

 is a "morphological prefiguration" in regard to the future, a " morphological representation" in 

 relation to the past, and a " morphological equivalent " in comparison with the individuals of other 

 series whicb have attained the same degree of development. 



2 The homologue of these and of some earlier inner whorls may be seen in PL XLIX, figs. 8, 8 a, 

 and part figs. 8 J, 9, 9 a. A portion of fig. 8 seems to indicate a much earlier ancestral form, but the 

 correctness of the ontogenetical record may have been falsified by the " partial or modifying action of 

 earlier inheritance" (p. 289). 



3 In the various stages of retrogressive development the species of Sonninia are the morpho- 

 logical equivalents of the species of Amaltheus, only they are a much more comprehensive series. 



4 In treating of some forms of this genus in his ' Amm. Schwiibischen Jura ' Quenstedt may be 

 said to have used names to distinguish each different form, but he employed a combined trinomial 

 and binomial system, e. g. Ammonites Sowerbyi, Am. Sowerbyi ovalis, Am. Soiverbyi insignoides, Am. 

 arenatus. The generic name Sonninia dispenses with the frequent repetition of' Ammonites Sowerbyi 

 in fact, it takes the place of this term, and something more ; because while Quenstedt wrote 

 Am. Sowerbyi and .4m. arenatus without any indication whether arenatus was closely allied to Sowerbyi, 

 or was, say, one of the Sumphriesianum-gr oup, I write Sonninia arenata, Sonninia Soiverbyi, and gain 

 the advantage of at once showing the true relationship of the two forms. In the same way Sonninia 

 ovalis, Sonninia insignoides show that these species belong to the Soiverbyi- group quite as effectually 

 as the cumbrous Ammonites- Sowerbyi-t'ormula. Further, it removes the false impression that these 

 species are necessarily more closely allied to Soiverbyi than arenatus is. 



