of certain species of Willow. — Part 2nd. 253 



No. 18. Gall S. ovulum, n. sp. — On S. humilis. Undistinguish- 

 able both internally and externally from S. ovum n. sp. But for the 

 tact that the larvae differ in color, and that, of the five species of willow 

 found near Rock Island, 111., this type of gall occurs only on S. humi- 

 lis and S. cordata — two willows which are, according to Mr. Bebb, very 

 distinct — and never, as I have carefully observed, on S. discolor — 

 which is on the same authority, very closely allied to S. humilis, the 

 species <m which S. ovulum is found — I should not suppose S. ovulum 

 to be a distinct (phytophagic) species from S. ovum. Possibly, indeed, 

 it may not be so • and to determine doubts it is better to await the dis- 

 covery of o 9 imago. Besides the three bushes of S. discolor men- 

 tioned above, (Proc. Ill, p. 589,) I have since discovered and examined 

 closely several dozens. This gall was rare in 1864 — 5 and 1865 — 6, 

 but common in 1863 — 4. Not local, but generally distributed. De- 

 scribed from 30 specimens. 



Larva. On August 30 I compared 6 larvae, freshly taken from the 

 gall S. ovulum, with 6 freshly taken from the gall S. ovum ; and while 

 the latter were all decidedly yellowish, the former were all decidedly 

 pale greenish. In other respects they did not differ perceptibly, and 

 both had free use of their legs. 



Pupa and Imago unknown. 



JVo. 19. Gall S. nodus, n. sp. — On S. longifolia. A mere gradual enlargement 

 of n twig from 1 more than its norma] diameter up to twice its normal diameter, 

 almost always without any abnormal roughness on the external bark, and al- 

 ways not confined to one side only of the twig. General color that of the twig. 

 When cut into, Aug. 28, the interior of each gall is found to be pithy, and to 

 contain 1 — 3 larvse in separate cells. Frequently, on a piece of a twig C inches 

 long, 2, 3 or 4 of these galls are placed at irregular intervals. Xo appearance 

 internally of any transverse platen or transverse fibres as in S. ovum and S. ocu- 

 lutn. Length .75 — 1.50 inch; diameter .10 — .2.5 inch. Described from 31 affected 

 twigs. Abundant but very local. Very like the Cecidomyidous gall S. nodulus 

 on the same willow, {Proc. &c. Ill, p. 000.) but is much larger, is polythalamous 

 instead of monothalamous, and occurs near Rock Island, 111., in quite a different 

 locality. Analogous willow-galls are made in Europe, not by a Euura, but by 

 several small species of Nematus. (Westw. In trod. II, p. 105.) 



Larva, Aug. 28, the larva is 20 footed, of a pale greenish white color, with the 

 mouth dark and the usual dark eye-spots. Length about .15 inch. On April 2, 

 a larva (1 specimen) cut out of a gall gathered in the preceding August, was 

 whitish, with a testaceous head and the usual eye-spots. Hence it appears, that 

 some larva-, at all events, do not go underground to pass the winter, but under- 

 go their transformations in the gall, and also that the larva does not pupize till 

 the following spring. 

 Puri I'm' .- \ V)1 . 



Imago. Euura s. nodus, n. sp. — % Differs from % Euura s. ovum only as fol- 

 lows : — 1st. The pale color is bright honey-yellow, not greenish-white, through- 



PHOCEBDIHGS EM, SOC. I'HILAD. DECEMBER, 1866. 



