SCUDDER ON TEETIARY INSECTS. 539 



Corydalus, itself the largest of all 'kno'w n Sialina. It (an bardly be 

 doubted that it must have been at least double the size of the living 

 type. The number of eggs laid is about or nearly the .same as in Coryda- 

 lus, presuming, in either case, all to be laid at once. 



Compared with the eggs, the albuminous substance surrounding them 

 is much softer, more or less friable, and rather easily removed, being 

 everywhere composed of fibers running in the same direction as the lon- 

 gitudinal axis of the egg. The weathering of the specimens has been 

 such that in several instances the whole albuminous cap has been 

 removed, and in others a large part also of the interovular jDartitions, 

 leaving the eggs standing erect, separated, each from its neighbors, by 

 from one-third to one-half its own thickness. In many cases, the eggs 

 can be pulled from their cells ; and, although frequently flattened, they 

 may be studied almost as well as if living. The eggs have an average 

 length of 2.6'"^ and a central width of 0.6™'" j they are nearly cylindrical, 

 but fciintly arcuate, slightly attenuated at the anterior extremity, and 

 slightly tumid on the posterior half, at the tip of which they taper 

 rapidly, rounding oft' to a rather broadly convex extremity, which is 

 flattened or often sunken in a circular central space 0.1™™ in diameter, 

 outside of which the surface is rather profusely filled with very shallow, 

 obscure, circular pits, averaging 0.01™™ in diameter. The anterior oxtre. 

 mity terminates in a slightly elevated, thin, subtuberculate rim, inclosing 

 a terminal portion, whose surface gradually rises centrally to form a 

 truncated cone, and is pitted with saucer-like depressions, gradually 

 diminishing in size up the sides of the central extension ; the latter is 

 about as long as the breadth of its tip ; its extremity, 0.04-0.055™™ in 

 diameter, is more or less sunken, with a central circular pit (the micro- 

 pyle) 0.01™™ in diameter ; while the rounded margin of the extension is 

 made more or less irregular by the saucer -like depressions which sur- 

 mount it, but have now become of extreme minuteness. This structure 

 of the anterior extremity of the egg agrees with what was ijreviously 

 known of the egg of Sialis, but no mention of the elevated point was 

 made in Mr. Eiley's description of the egg of Gorydalus. It occurs there, 

 however, as I find by examination of eggs he has kindly sent me. These 

 eggs of Gorydalus also show the sunken space at the posterior end, and 

 the sides of the egg are marked nearly as in the fossil; the surface of the 

 latter being broken up by scarcely elevated slight ridges into obscure 

 transverse hexagonal cells, one-tenth of a millimeter long (across the 

 egg) and one-fifth as broad, those of adjoining rows interdigitating. 



In the disposition of the eggs, also, these masses differ from those of 

 Corydalus, for they are arranged in a radiating manner around the lon- 

 gitudinal axis of the ootheca. All of them partake of this arrangement, 

 even when, as rarely happens, there are two layers in place of one over 

 parts of the mass ; in no case are any of the eggs packed in irregularly, 

 as is the case with a portion of those of Gorydalus, accordiug to Eiley. 

 As in Gorydalus, however, the posterior ends are those which are 



