48 ILLINOIS BIOLOGICAL MONOGRAPHS {366 



12(11) Subspiracular and pedal lines without black spots; spots on subdorsal lines small, 

 often not distinctly tapering caudad; tenth abdominal tergum with a pair of large 

 black spots; length, 20 mm.; G-133 Neodiprion, sp. 4. 



MONOCTENUS DAHLBOM 



Larvae rather small; length about 15 mm.; body slender, dorsum 

 with diffuse brownish shade or with longitudinal stripes; third abdominal 

 segment with annulets 2 and 4 with setae and glandubae; head as in Neo- 

 diprion except that setae are minute and sparse; clypeus and lab rum with 

 two setae on each side; labrum with small crescentic median emargination; 

 maxillary palpi large, rather slender, segments 1-3 ring-like, subequal in 

 length but successively smaller in diameter; galeae and laciniae as in Neo- 

 diprion; labial palpi rather slender, its segments subequal in length; man- 

 dible with one mandibular seta; antennae with segment 1 complete, very 

 narrow, oval, segment 2 flat, incomplete, irregular, segment 3 peg-like, 

 erect; glandubae conical, distinct; setae microscopic; sublateral lobes not 

 well developed; annulation typically (1, 2), (3, 4, 5, 6), anal setae numer- 

 ous, short, and minute; telson with glandubae obsolete. 



MacGillivray established in 1906 the subfamily Monocteninae for 

 the genus Monoctenus associating it with the Cladiinae and Nematinae, 

 thus deviating from the universal practice of regarding the genus Monoc- 

 tenus as a member of the subfamily Diprioninae or its equivalent. On 

 the basis of the venation, MacGillivray's contention is quite justifiable, 

 and it is most interesting to know what larval characters would indicate 

 in regard to the relationship between Monoctenus and Diprion and its 

 allies. Marlatt (1887) published notes on the immature stages of Monoc- 

 tenus unicolor but his descriptions do not touch the detailed anatomy 

 necessary for the definition of the genus. Recently, however, I was 

 fortunate enough, thru the courtesy of Mr. Rohwer, to examine a speci- 

 men belonging to the United States National Museum which Rohwer 

 considered to belong to a new species of Monoctenus. A careful study 

 of this larva convinced me that [so far as this species is concerned] there 

 are no essential differences between the larvae of Monoctenus and those 

 of the typical Diprioninae to justify the creation of a new subfamily. 

 For this reason I have followed the universal practice and decided to 

 treat Monoctenus as a member of the Diprioninae. 



Monoctenus n. sp. Rohwer. — Length, 14 mm., head-width 1.5 mm.; 

 head brownish; body on dorsum dorsad of spiracular lines, segments of legs, 

 episternum and epimeron, deep brown; glandubae elongate, conical, 

 minute, brownish at tip; on cedar. 



A specimen bearing the label "5419 Sawfly on cedar, Cadek, Mo., 

 June 10, 1892." 



