■86 THE LEECHES OE MINNESOTA 



Placobdella rugosa (Verrill) Moore. 



(Plate I, fig. 6, 9) 



Clef sine ornata var. rugosa Verrill (1874) 

 Placobdella rugosa Moore (1901) 



Description — Placobdella rugosa is a large leech, nearly or 

 quite equalling P. parasitica, although the great majority of ex- 

 amples met with average considerably smaller than that species. 

 In form it is even more depressed, starving individuals being 

 scarcely thicker than a card, very broad and leaf-like. The head 

 is essentially similar to that of P. parasitica but as this leech does 

 not extend itself as fully as that it is seldom seen in the distinctly 

 expanded state. The caudal sucker is large and elliptical rather 

 than circular, the antero-posterior diameter being slightly greater 

 than the transverse. An important characteristic is the presence 

 of numerous large rough cutaneous papillae on the dorsum. The 

 principal ones are constant in arrangement but the number of 

 smaller ones is quite variable. Most characteristic and conspicuous 

 are five on each neural annulus, median, supra-marginal and inter- 

 mediate in position and forming five longitudinal series as far 

 caudad as somite XXIII, posterior to which the median papillae 

 become greatly reduced in size and overshadowed by paramedian 

 papillae in line with the dorso-median sensillae. On ai the papillae 

 are all relatively small while flj bears some of large size inferior 

 only to the largest on as. The integument is translucent. 



Somites I and II are uniannulate and always distinctly sepa- 

 rated; III is biannulate with a faint furrow usually discernible 

 across the larger anterior annulus, on the posterior division of which 

 are seen the small compound eyes, often included in a common 

 pigment mass. Somite IV is triannulate dorsally but ar/aj is less 

 distinct than the other furrows; V is triannulate dorsally, biannu- 

 late ventrally. The fully triannulate Semites are VI to XXI II in- 

 clusive, and this species shows in a much less convincing way the 

 transitional steps between biannulate and triannulate somites. In 

 all of the complete somites a noteworthy feature is the lack of 

 alignment between the dorsal and ventral Furrows, as a result of 

 which a.2 is the longest annulus dorsally but the shortest ventrally. 

 ( >f the posterior simpler somites, XXIV is triannulate dorsally with 

 a; of very much smaller relative size and incompletely separated 



