358 PROCEEDINGS OF THE ACADEMY OF [PaRT II 



1860 Dislorsio septemdentata Gabb, Jour. Acad. Nat. Sci., iv, p. 380, pi. 



67, fig. 21. 

 1873 Triton grasi (Bellardi), in d'Anconi, Malac. Plioc. Ital. 11, p. 70, pi. 



16, fig. 1. 

 1909 Distorsio gatunensis Tuola, Jahrb. K,-K. Geol. Reichsanst. Iviii, 1908, 



p. 700, pl. 25, fig. 10. 



Recent monographers have lumped all the hving forms under one 

 or other of the above names, but there seem to be three or four 

 valid species among them. The principal synonomy of the recent 

 forms is given below; that of the European Miocene species has 

 been duly set forth by Bellardi. -^^ 



Distorsio reticidata Link. Includes acuta Perry, cancellinus 

 Lam. (?), rmdus Dillw., pusilla Pse., cancellinus Reeve. 



This species is the common Indo-Pacific form. Its chief, and so 

 far as we know, invariable character is the presence of a prominent 

 and somewhat gibbous bilirate ridge or keel at the shoulder, on the back 

 of the shell. 



The strong entering fold on the upper part of the parietal wall 

 is more distant from the oblong tubercle above it than in the 

 Antillean species, and the typical form has a wider sinus on the 

 columella, and less prominent third tooth within the outer lip. 

 Reeve's figure of cancellinus (Conch. Icon. pl. 12, fig. 45) well re- 

 presents the face of the shell. 



The Murex cancellinus, attributed to Roissy by various authors, 

 was originally described by Lamarck, the account in Sonnini's 

 Buff on being merely a repetition. Lamarck described the shell as 

 a Grignon fossil, but there cannot be much doubt that it was either 

 a stray bleached example of one of the recent species or the European 

 Miocene D. tortuosum. As he refers to Martini's figures, those 

 who used the name for the recent D. reticulata are not without 

 justification; but in view of the uncertainty attending it, and its 

 later date than Link's name, it had better be placed in the syn- 

 onymy. No later author has recorded M. cancellinus, or any 

 Distorsio, from the Parisian Eocene. 



D. decipiens (Rve.) is a smaller form with reddish apertural 

 callus and a series of four short folds on the parietal wall above, in 

 place of the two large ones of typical reticulata. The third tooth 

 of the lip is prominent; the back angular as in reticulata. While it 

 may turn out to be a subspecies of D. reticulata, the differential 

 characters are constant in the small series examined. 



2'- 1 Moll. Ter. Terz. Piemonte e della Liguria, I, 231. 



