314 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
which the sheU appeared, he says, "the posterior surface of the foot 
which, at first, was convex, now becomes flattened and develops a 
thin, horny operculum, with which the mouth of the shell can be closed." 
Pelseneer (10) figures the shell of a young Patella vulgata (Fig. 1) 
with as pronounced a coiled nucleus as one sees in the young of Fis- 
surella or Cemoria. Lang (6) says, "The 
cup-shaped shell of Fissurella is only sec- 
ondarily symmetrical, /. r. that Fissurella is 
descended from forms which possessed a 
spirally coiled shell. The same is the case 
with the Patellidae." 
Walter K. Fisher (2), in his admirable 
memoir on the anatomy of Lottia giganfca, 
savs that "Dr. Harold Heath has found specimens oi Acmaea sped rum 
and likewise of Nacella sp. less than a millimeter in length, which 
possess a tiny nautiloid coil, at the apex of the flaring shell. This 
larval coil is soon lost through decollation, and the familiar conical shell 
is left." In his summary Fisher says, "The Acmaeidae possess a 
larval nautiloid shell." In the above references therefore we have 
Fig. 1. 
definite statements that a coiled nautiloid shell first appears in Pafclla 
vulgata and Acmaea spectrum, and is characteristic of the family 
Acmaeidae. 
Patten's figure shows the beginning of what ajjpears to be a nautiloid 
shell and were it not for Pelseneer's figure of a definite coiled apical 
process in the young of P. vulgata, I should believe it to be the begin- 
ning of a blunt caecal-like cap without the suggestion of a coil, identical 
