THE NAUTILUS. 49 



The true habitat of Priotrochatdlo. constellata is the northern por- 

 tion of the Sierra de Casas, that of P. stellata the Sierra de 

 Caballos and possibly in its northern extension now called the 

 Sierra de Columbus. I do not know of any records of either 

 species being found on the opposite side of the river from its 

 true habitat. Due to the fact that P. torrel does not possess a 

 rapidly descending ultimate whorl, as in P. constellata, therefore 

 lacking that species' pagoda-form appearance, one would be in- 

 clined to suppose that it is most closely related to P. stellata, in 

 spite of its habitat in that region theoretically occupied only by 

 P. constellata. Admitting as a possible premise that P. constel- 

 lata and P. stellata are derivatives of a common ancestor; that 

 due to separation on opposite sides of the river Sierra de Casas, 

 the two species have assumed characters rendering them specifi- 

 cally distinct, there are then several possible explanations of 

 the origin of P. torrei. 1. A direct descent from the original 

 Priotrochatella stock isolated by geographical change in its own 

 particular habitat at approximately the same period as P. con- 

 stellata and P. stellata. 2. A more recent geographical separa- 

 tion from either P. stellata or P. constellata. In an attempt to 

 throw some light on this question I have examined the radulae 

 of three specimens of each of the three species of Priotrochatella. 

 That too much stress must not be placed on the value of the 

 radula as an important character in deciding specific values has 

 been repeatedly demonstrated. I nevertheless believe that suffi- 

 cient differences appear in the radulae of the species mentioned 

 to furnish some foundation for my belief that P. torrei, in spite 

 of its outward similarity to stellata, is probably more closely re- 

 lated to constellata. 



The name Priotrochatella was given as a subgenus by Crosse ' 

 to those species of Eutrochatella possessing an operculum similar 

 to that of constellata. Wagner' raises Priotrochatella to a genus 

 and includes the species constellata Mor. and stellata Vel. As 

 far as I know no figures of the radulae of Priotrochatella have 

 been published. 



- r-Tosse: J. (ie Conch., vol. 41. p. 88, 1893. 



8 Wagner: Denkschriften Akml. Wissenschaften. BarJ LXXVIT. p. 

 369, 1905. 



