228 THE GENERA OF NEMERTEANS. 



patch (black by transparency) occurs in front between 

 the two lines uniting the eyes. May be that it afterwards 

 shall turn out to be specifically distinct. 



40. Tetrastemma melanocephalum (Johnst.) Dies. 

 Synon. Ommatoplea melanocephala Mac Int. 



The yellow colour and the broad blackish-brown patch 

 on the head are characteristic for this species. It must 

 however be kept distinct from T. coronata with which 

 Mac Intosh held it to be identical; in Naples both species 

 occur and by the absence of any intermediate variety must 

 be regarded as distinct species. 



41. Tetrastemma coronatum (Quatref.) Hubr. 

 Synon. Polia coronata Quatrefages. 



A dark band , less broad than in T. melanocephala is 

 situated transversely between the anterior and posterior pair 

 of eyes. It is sometimes interrupted in the middle and 

 always readily distinguished from the dark patch which 

 is characteristic for the foregoing species. The colour is 

 never so decidedly yellow as in T. melanocephala. Numerous 

 specimens confirmed the necessity of distinguishing them. 



42. Tetrastemma diadema n. sp. 



Two white patches on the head (black when viewed by 

 transparency under the microscope) not due to a separate 

 pigment but to fatty globules in the integument. They 

 are very constant in form and dimensions; one is large 

 and quadrangular and reaches from the front pair of eyes 

 to near the hinder pair, whereas the other smaller one 

 is situated behind the posterior eyes. Generally two smaller 

 patches of the same nature occur towards the lateral mar- 

 gins of the head, whereas a transverse band oflightbrown 

 pigment runs across the head and unites the two posterior eyes. 



Numerous specimens proved this to be a reliable species, 



Pi'otes from, the Leyden ÜMxiseuiii. 



