THE NAUTILUS. 148 



but with fewer whorls. The specimen named by liaymond does not 

 show plication. 



3. Borsonia dalli Arn. Only four specimens are found under this 

 label. Two show no plication, and the others, though plicate, have 

 one and three more whorls than the type. In tliis case Arnold's 

 figure does not agree with the description. 



4. DriUia merriami Arn. Of ten specimens all agree with the 

 author's figure and description in surface markings. iSix have the 

 form of B. bartschii but differ in the transverse ribs on the body 

 whorl, and one has a plication on the columella. Four slender forms 

 agree with the type, but one has nine whorls and two have plications 

 like Borsonia. 



5. DriUia renaudi Arn. Of 27 specimens examined, 10 agree in 

 form and surface markings with B. bartschii. One has columellar 

 fold almost obsolete, 20 agree with the type in the absence of ribs on 

 the body whorl, but have from one to three fewer whorls, while 8 

 have faint plications on the inner lip. 



6. DriUia pedroana Arn. Of 20 specimens examined, two broken 

 ones agree witli Arnold's figure and description, but the others have 

 from one to three more whorls. Half ot these have a distinct sutural 

 band, while the rest approach the next. 



7. Spirotropis smithi Arn. Of 150 specimens examined, 10 agree 

 in form and surface markings with D. pedroana as above noted in 

 the perfect forms. Several have faint spiral lines on the body whorl 

 like the last. One half exceed the type in size, approaching .50 mm. 



8. Pleurotojna perversa Gabb. About GoO individuals were 

 brought together under this name in the Rivers Collection, and 

 simply because they happened to be sinistral forms. About half are 

 very robust, approaching 60 mm. in length, with broader, more 

 ventricose whorls than the figure and description, but among these 

 are a few which duplicate the dextral S. smithi. The smaller forms 

 noted as " young " in the collection are more slender with flattened 

 volutions, and absolutely duplicate, in sinistral form, the dextral 

 types of D. pedroana, B. daUi, and B. hooveri. 



These notes lead to rather interesting conclusions : 



1. The predominating type in these beds is the sinistral. All of 

 the smooth dextral forms, B. dalli, D. pedroana, and S. smithi, have 

 exact counterparts with reversed coil. 



2. This duplication of dextral and sinistral forms minimizes the 

 value of reversal of coil as a specific distinction in this group. 



