482 FREDERICK IV. SARDESON 



shorter cones and the spiral coils, the manner in which the 

 spirals arose may be interpreted from the phenomenon seen in 

 the Cambrian Gastropoda, where ontogenically the apex of the 

 shell coiled most; and the conclusion is drawn that phylogeni- 

 cally the apex coiled first and the "body whorl" last. This is 

 contrary to the view which has heretofore been held. 



Possibly the example of uncoiling spiral shells in later geo- 

 logic ages and the embryonic evidence of the Recent larval 

 coiled shell have been applied too hastily to the interpretation 

 of Cambrian Gastropoda. In the Cephalopoda the coiling is 

 better known and affords fine examples for comparison. The 

 correspondence of stages in phylogeny and ontogeny among the 

 Ammonoidea, where the straight, curved, coiled, and uncoiled 

 structure follow in order, is well known. In the Nautiloidea 

 there very early occur both the coiling and the supposed uncoil- 

 ing ; and, indeed, there are such types as Ophidioceras, which 

 is convolute in the middle and uncoiled at both ends. In this 

 case the interpretation of the apical end as progressive and the 

 apertural end as retrogressive might be taken as not sufficiently 

 proved to serve as evidence. The Belemnoidean Recent genus 

 Spirula is seen to have derived from a straight phragmocone, but 

 is apically coiled, i. e., it is in a genetic sense coiling, but appears 

 uncoiling. After all, the Cephalopoda afford indecisive results, 

 even if it was safe to apply a cephalopod measure to the grastro- 

 pods. If anything fitting this case is indicated by them, it is 

 that even within the group Gastropoda such uncoiling shells as 

 Vermetus do not prove the rule. 



The "Studies of Gastropoda"^ by Grabau has come to hand 

 after the above paragraphs were outlined and it may serve to 

 indicate how firmly the view opposite to that here presented is 

 held generally. Grabau unhesitatingly interprets Platyceras 

 primaevum Bill., as a phylogerontic unrolled type.^ He further 

 cites Ordovician species as phylogerontic, following Ulrich's 

 figures and descriptions in these, where, in the first instance, my 

 collections lead me to conclusions widely different from those of 

 Ulrich. We have to do with highly variable shells of fewer 



^ Atnerican Naturalist, Vol. XXXVI, pp. 917-45. ^ Op. cit., p. 938. 



