136 



and its two vai'ieties the rosti-uin is most tiincs tuothed ; 



the formula — - — , not rare in the variety iittenitedid^ is, aniong 

 o 



the Black Sea specimens, only presented by ene single specimen, 



8 — 1 

 bnt, on the contrary, the fornuüa — ' is observed in 14 per 



cent. of the specimens. Also, like in the typical form and in the 

 variety intermedia, the upper margin is usually armed with 

 ek/Jit teeth, viz. in 69 per cent. of the specimens, more rarely 



i. e. in S'/j pt'i' cent., with >^/>/r: in the variety //#Y('r///c(//V^, however, 

 in 20 per cent. of the specimens the rostrum was armed with 

 nine teeth. In 80 per cent. of the specimens only one apical 

 tüoth occurs, as in the typical species and as in the variety infer- 

 inedia^ but in 18 per cent. the rostrum presented two apical teeth, 

 in a larger percentage, therefore, than in the specimens froni the 

 west coast of Europe; only in one young individual there was 

 no apical tooth at all. In 77 per cent. of the specimens the lower 

 margin is armed with three, but in 23 per cent. with four teeth : 

 while a rostrum with 4 teeth on the lower margin appears, in 

 the typical species and in the variety inteniiedia^ as a grcat exception, 

 in the variety cïef/cms no less fJia» '^3 prr c(nd. of the specimens are 

 (irined /rith foiir teeth on the loicer nutn/iii^ a fact wdiich there-^ 

 fore appears to be characteristic of this variety. Specimens with 

 only two teeth on the low^er margin do no more occur. In the 

 larger specimens from the Bay of Sebastopol fhree teeth are 

 situated on the carapace, the 4th tooth just before the orbital 

 margin, but in the youngest individuals, measuring 20 mm. or 

 less, only tiro teeth are placed on the carapace and the 3'l tooth 

 either just above or just before the orbital margin. The l^t tooth 

 of the upper margin is 1 'Z^— P/j-times as far distant from the 

 posterior margin of the carapace as from the orbital margin, 

 ïhe shape of the rostrum is also characteristic, because, in the 

 Black Sea specimens, the distal half is invariahly and rather 

 stro}ir/li/ treiid'nK) Hpirards. 



