76 THE CONSTITUTION OF THE GASTROPOD PROTOCONCH, 



9. The combination of these two factors has caused the 

 mollusc to I'otate through an angle of 90" within its shell, 

 thereby coming into a position in which the close spiral might 

 be maintained. 



10. The MumUlate, Eccentric, and Tumid Protoconchs will 

 generally be found to be correlated with an absence of free 

 pelagic existence ; the converse, however, will not hold true ; 

 the absence of these types of protoconch does not necessarily 

 indicate a free pelagic Veligtr stage. 



11. The distribution of marine species has been determined, 

 in large measure, by the length of the pelagic existence of the 

 Veliger; and hence in as far as the size of the protoconch, 

 number of its whorls, etc., is a measure of the length of the 

 pelagic existence, so also will it be in many cases a measure of 

 its distribution- 

 is. The characters of the Anaueanoconch, or that portion 



of it which constitutes the first whorl or two of the true conch, 

 may often be used to outline the more recent evolution of a 

 species. 



The Genus fSsPTA. 



In the paper above referred to, Dall (7) separates those 

 species of the genus Cymatiuiit which resemble Ci/niatium 

 tritonis Linn., i;nder the name of Septa, giving the name full 

 generic rank. He says (p. 126) : "In considering the arrange- 

 ment of the members of the group (Frog-shells and Tritons') 

 the dentition, the protoconch and nepionic shell, and the 

 generic rank. He says (p. 126) : "In considering the arrange- 

 ment, and with the possible exception of the last all are more 

 important than conchological (conchic ?) sculpture and form." 

 The meanings of the terms "protoconch" and "nepionic 

 shell" as used by him are peculiar; it appears that he differs 

 from all other conchologists and malacologists in restricting 

 the term protoconch to the caliculus, and applies the term 

 "nepionic shell" to the remainder of what is usually termed 

 protoconch. This interpretation of his meaning is drawn 



