8 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 



GEOTJP 1. 



Group 1 contains species normally restricted to rivers which have 

 rocky beds and such obstructions as bridge piles, piers, and, in time 

 of floods, partly submerged trees. These species deposit their eggs 

 at the level of the water, or just below, on any convenient surface, 

 such as the bare portions of rocks, sunken posts, and collections of 

 water-worn debris, always where the current is exceedingly swift. 

 Eggs have never been found by the writer on any surface that was not 

 smooth or that was at all covered by moss, algae, or other aquatic 

 growths. Of the five species whose methods of oviposition are dis- 

 cussed in this article, S. pictipes alone belongs in this group. The 

 oviposition and early life history of this species were first described 

 by Dr. W. S. Barnard in the American Entomologist in 1880. He 

 states that the eggs are long ovoid in form, and gives a figure showing 

 them deposited in a vertical position. He also states that the young 

 larvae were issuing from the eggs deposited on the rocks above the 

 water line and were passing down into the water to begin aquatic life. 

 If this was the case, the eggs must have been moistened continually 

 by the spray and not left in a dry state, as is implied, the reason for 

 which surmise will be discussed at length farther on. 



The eggs of this species which were found by the writer seemed 

 to have been deposited indiscriminately in a horizontal as well as in 

 a vertical position. The angles appeared rather broadly rounded. 

 (PI. Ill, fig. 6.) Surrounded by a viscous substance known as the 

 matrix, in which they are fairly evenly distributed, they are laid 

 normally in masses on the smooth surface of the rocks just below the 

 level of the water. The matrix is brownish yellow at first, after- 

 wards turning brown. Usually several females will oviposit in the 

 same spot, causing the layers to overlap. 



GROUP 2. 



Group 2 is made up of species which are peculiar to small streams 

 with less force of current and with only submerged herbage or occa- 

 sional small collections of sticks and stones to serve as a place for 

 the attachment of the immature stages. As a general rule the situ- 

 ation selected for oviposition is a grass blade bent at right angles and 

 trailing just at the surface of the water and with its surface continu- 

 ously moistened. 



S. vittatwn almost invariably oviposits on grass blades in small 

 streams. The eggs adhere to the grass blades by a creamy viscous 

 matrix entirely covering the eggs. This matrix turns yellowish 

 brown on the second day and becomes gradually darker until the eggs 

 hatch. The eggs are laid in a single layer, as a rule, very closely 

 together. Several females often select the same situation and, as in 

 the case of pictipes, the layers often overlap one another. 



