NEUROPTERA— PLANIPENNIA— SIALINA. 151 



could be reached by the abdomen of the insect while resting upon a stone 

 or overhanging twig. In this medium the albuminous secretion would ex- 

 pand to the utmost ; if the bunch of eggs remained undisturbed, it would 

 present us with the more regular hirudiniform masses thai have been found ; 

 if rolled about by the disturbance of the waters, the two halves would curl 

 toward each other more or less closely, forming a subcylindrical mass, and 

 inclose between their approaching walls more or less of the mud in which 

 they are rolled. This is exactly the appearance of most of them now, 

 inclosing the same substances as that within which they and the accompany- 

 ing Bulimi and other fresh-water moUusks lie embedded.' 



These masses differ from those of Corydalus in the extraordinary amount 

 of albuminous matter which surrounds both the entire mass (Fig. 16) and 

 each individual egg (Fig. 7). This is perhaps to be explained by the 

 medium in which they appear to have been laid, and will in part account 

 for the vast size of the ootheca, which are much larger than any mass of 

 insect eggs which I can find noticed. The size of the mass, however, is 

 also due to the greater magnitude of the eggs themselves, which are twice 

 as long as and proportionally larger than those of Corydalus (Figs. 17, 21), 

 and lead to the conviction that we are to look in the rocks of the Laramie 

 Group for an insect of great magnitude, closely allied to our Corydalus, 

 itself the largest of all known Sialina. It can hardly 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 Corydalus, 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 easily removed, being everywhere 

 composed of fibers running in the same direction as the longitudinal axis 

 of the egg. The weathering of the specimens has been such that in sev- 

 eral instances the whole albuminous cap has been removed, and in others a 

 large part also of the interovular partitions, leaving the eggs standing erect, 

 each separated 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, al- 

 though frequently flattened, they may be studied almost as well as if living. 



The eggs (Fig. 21) have an average length of 2.6""" and a central 



' The deposit in which they occur is a fresh- water one; but Mr. Lesquereux informs me that brackieh- 

 water forms are found both above and below them. For details concerning the age of the deposit and 

 the fossils associated with Corydalites, see the article by Dr. C. A. White, quoted above. 



