418 THE CHICAGO ACADEMY OF SCIENCES. 



Length. Width. Aperture length. Width. 



36.00 29.00 27.00 17.50 mill. 



32.00 25.00 24.50 17.50 " 



29.00 19.00 20.00 10.50 " 



76.00 19.00 21.00 11.00 " 



26.50 19.00 19.00 10.00 " 



26.50 19.00 19.50 12.00 " 



25.00 18.50 19.00 10.00 " 



25.00 19.00 19.00 11.00 " 



22.50 17.50 17.50 9.50 " 



TYPE : Destroyed in the Portland fire of 1866. 

 TYPE LOCALITY: Second Eagle Lake, Aroostook Co., Maine. 

 ANIMAL: Not differing externally from that of typical emar- 

 ginata. 



JAW : As in emarginata. 



RADULA : (PL IX, fig. G) . Formula : ^Vh]*+H4+ V+*^+6 2 4 

 (35-1-35) in 130 rows; central tooth long, narrow, unicuspid; lateral 

 teeth wide with a subquadrate base of attachment; reflection large, 

 bicuspid, the mesocone very large, symmetrically rounded and terminat- 

 ing in a sharp point ; the ectocone very small, rather wide, the extremity 

 rather sharp and in some cases pointed inward toward the inner cusp ; 

 intermediate teeth tricuspid, the mesocone rather long, wide, the ento- 

 cone large and placed near the distal end of the reflection, the ecto- 

 cone smaller and placed higher up; the thirteenth tooth has a smaller 

 denticle above the ectocone; the marginal teeth are long and narrow, 

 the distal end of the reflection 3 to 4 cuspid with two denticles on the 

 outer edge of the reflection. In one specimen examined the inter- 

 mediate teeth began at the fifteenth tooth but this membrane was evi- 

 dently abnormal. 



GENITALIA: The genitalia of mighelsi are in all respects like 

 those of emarginata. 1 Specimens from Square Lake inlet measured 

 as follows : 



Penis- Ret. mus. Ret. mus. Vas. Prost. 



Penis. sac. penis, penis-sac. def. duct. Rec. sem. Shell. 



2.00 4.50 1.50 1.50 26.00 6.25 6.00 19.00 



2.00 5.00 2.50 3.00 24.50 6.25 6.00 



1.80 3.00 2.25 2.25 25.00 6.00 5.50 



A study of the genitalia clearly indicates the close relationship 

 between emarginata and mighelsi. 



>It will be noted that the figure of the genitalia of emarginata differs 

 radically from those previously described by the writer. This is due to the 

 fact that they were drawn in a different position (the former figures being 

 from the side), the organs are separated and better magnifying glasses were 

 used which more clearly Indicated the shape and position of the different 



