or Lower Cambrian of the Atlantic border province of North America. 
That it is not the most primitive type of gastropod is suggested by the con- 
sideration that the earliest stage . . . . of the protoconch is not 
coiled, but rather cap-shaped like modern Patella. Such primitive types 
are found in Lower Cambrian species which have yariously been referred 
to Platyceras, Scenella, or Stenotheca, owing to the want of sufficient 
characteristics to define their exact relations.” (22. 
From the above it appears that the early protoconch stages indicate 
an aneestor of the simple, smooth shelled, umbilicated type exemplified by 
Straparollina, and that this is actually the only type of coiled gastropod 
characteristic of the basal Cambrian. It is also likely from paleontolog- 
ical evidence that the very earliest type of gastropod possessed a conical 
or cornucopia-shaped shel} of the Scenella type... Such an ancestry is, 
according to Grabau, suggested by the cap-shaped earliest stage of the 
protoconch.? 
One of the most completely worked-out cases of recapitulation among 
Gastropoda that has come to my knowledge is that of the races of Athleta 
petrosa Con. and its allies. The phylogeny of this group of gastropods 
has been very fully studied by Burnett Smith (54), from whose paper 
the following account is dvawn. 
1Sardeson (50) suggests that the gastropod ancestor was an ‘asymmetrical 
long conical shell’ of the pteropod type. He may be right, but even so, I do not 
see that his conclusion would in the least invalidate the conclusions of Grabau in 
regard to the phylogenetic significance of the protoconch, although Sardeson seems 
to think so. Grabau says very plainly that the coiled shell is probably not the 
most primitive type of shell, and he points out the fact (quoted above) that the 
initial portion of the protoconch is cap-Shaped and may indicate some such remote 
ancestor as the Cambrian forms referred to the genera Platyceras, Stenotheca, and 
Scenella. Whether this patelliform ancestor was in turn derived from a long 
conical shell, or whether on the other hand the coiled type of shell was derived 
directly from the “long conical’’ shell without the mediation of a _ patelliform 
ancestor, does not materially affect the conclusions that at a very remote time 
a coiled gastropod radicle was established from which practically all modern 
gastropods were derived. To my mind the conclusion that the ultimate ancestor 
of the Gastropoda was a “long conical” shell is by no mears established. 
2 Burnett Smith (55) concludes from a study of the Tertiary species of the 
genus Athleta that ‘“‘we can say for this restricted normal group at least that the 
apex is not only a variable feature, but the most variable feature which the shells 
furnish.” In a footnote he says “The author is thoroughly convinced that the 
features of the apex must be used in classification with great caution.’’ The varia- 
tions which he cites in this and other papers (54, 55, 56) seem to be chiefly in 
the size of the protoconch, and the degree to which acceleration has caused conchal 
characters to appear in the later protoconchal stages. His caution, however, in 
regard to the classificatory value of the protoconch, should put students of the 
gastropods on their guard against a too free use of this portion of the shell in the 
establishing of genera. 
[21—23003] 
