138 [June, 



consider the two species distinct. Herr Friederichs was, however, not 

 acquainted with the fact that Edwards had established the distinction 

 so far back as the year 1890. This species is at present without a 

 name, it having been, as previously stated, erroneously identified 70 

 years ago by Suffrian as the opacus of Sahlberg. I am, therefore, 

 very pleased to connect it with the name of Mr. Jas. Edwards, to 

 whom is due its first certain discrimination. Suffrian' s characters for 

 distinguishing marinus and " opacus (Stettin, ent. Zeit., 1842 and 

 1846) were correct so far as they went, but did not go far enough. 



EXPLANATION OF PLATES IX, X. 



Both the dorsal and ventral aspects of the sedeagus are figured : 

 the ventral is marked a, the dorsal aspect b. The chitinous portions 

 are shown by the aid of dots, the parts left undotted are membranous. 

 It will be noticed that no orifice is shewn, but the manner in which 

 the duct is extruded is shown in the illustration accompanying the 

 second page of this paper. 



The figures have been drawn with the camera lucida by my 

 daughter, Margaret Annie Sharp, and she has taken much pains to 

 delineate correctly the amount of ehitinisation at the sides and tip of 

 the ventral aspect of the median lobe. This character is of great 

 interest and importance because on it depend ultimately the modifica- 

 tions in form of the median lobe. It is the most difficult point in 

 this study, because the limits of the ehitinisation are only indefinite 

 when the example is immature. Potash should be used with great 

 caution in making the preparation, as it is liable to cause shrivelling 

 and distortion. 



Figs. 1. — G. minutus; a ventral, b dorsal. 



„ 2. — „ urinator ; a „ b „ 



„ 3. — „ natator ; a „ b „ 



„ 4. — „ „ var oblitus ; a ventral, b dorsal. 



„ 5. — „ suffriani ; a ventral, b dorsal. 



„ 6. — „ elongatus ; a „ b „ 



„ 7. — „ colymbus ; a „ b „ 



„ 8. — „ striolatus ; a „ b „ 



„ 9. — „ bicolor ; a „ b „ 



„ 10. — „ marinus ; a ventral with basal piece ; b dorsal. 



„ 11. — „ edwardsi ; a „ b dorsal. 



„ 12. — „ opacus ; a „ b „ 



„ 13. — „ edwardsi, female styles. 



„ 14. — „ colymbus, male, shrivelled specimen for comparison 

 with figs. 7 ; a ventral, b dorsal. 



Brockenhurst : 



February 23rd, 1914. 



