OLDEST KNOWN INSECT-LARVA. 435 



preceding- as well as its ordinary form is shown in figs. 1, 10 and 16, where it is quad- 

 rate Imt well rounded, tapering and about two-thirds as large as the preceding joint. 

 In some cases, however, as in fig. 9, it is very small, and its separation from the preced- 

 ing joint hardly noticeable, while at the other extreme, as in fig. 7, it is scarcely smaller 

 than the preceding segment and longer, if anything, than broad. But the most inter- 

 esting feature in this segment is the discovery in a few specimens, as in figs. 9 and 14 

 and to a slight degree in figs. 2 and 1G, of appendages. There is an outer pair of 

 slender styles, a little shorter than the penultimate segment, directed backward and a 

 little divergent; and a much shorter pair, or perhaps only projections of the pygidium, 

 lying between the longer styles. 



As there is not a single specimen among the hundreds I have seen showing a lateral 

 or even a partially lateral view, the insect could not have been cylindrical but must have 

 been considerably flattened. The variation in the general form of the specimens, as pre- 

 served, indicates a not very corneous or rigid integument, since the shape of single seg- 

 ments varies considerably. Yet the general form is as a rule so uniform (as appears in 

 fig. 8, where a number of specimens are exhibited just as they lie on the stone, much 

 better than my selection of other specimens to be drawn for some particular feature) 

 that we must consider the integument to have been at least coriaceous, and the varying - 

 proportions of single segments to depend, partly at least, upon the greater or less ex- 

 posure of the intersegmental membrane. 



When we come to consider the probable affinities of a larva having the structure 

 above described, we are at a loss. ISTo living form seems to be at all nearly allied to it. 

 It would appear on general grounds to be either coleopterous or neuropterous, and from 

 its aquatic habit to be more likely neuropterous than coleopterous; but further than this 

 one must tread largely on conjectural ground. The structure of the head, in which the 

 only recognizable appendages appear to be nearly or quite globular and chitinous, the 

 absence or extreme brevity of the legs in connection with a plainly flattened body, and 

 a terminal segment provided with cerei, are combinations and features very extraordi- 

 nary. The only coleopterous larvae which seem at all to remind one of their general 

 appearance are the Silphidae, all the larvae of which now known prey upon decaying 

 animal and vegetable matter or live upon fungi, and none are aquatic; the Lampyridae, 

 which are equally out of the question; and the Ileteroceridae, which have no terminal 

 appendages. These larvae, besides having a genera] form somewhat resembling that of 

 Mormolucoides, have a flattened body, 1 short legs, and the Silphidae also a small head 

 and distinct anal cerei, besides posterior lateral extensions of, or appendages to, the ab- 

 dominal segments; but they have <also comparatively small and tender mouth-parts; and 

 the Silphidae stout, jointed antennae of considerable length, while their legs are usually, 

 at least, as long as the greatest width of the body; and besides the ordinary nine seg- 

 ments of the abdomen, there is in the Silphidae the strongly protruding pipe-like pygid- 

 ium, for which there is no homologue in Mormolucoides, unless the inner pair of cerei 

 be taken as representing a completely forked pygidium. When we add to these differ- 

 ences the peculiar habitat of the living Silphidae, and the similar terrestrial haunts of 



1 In Heterocerus it is cylindrical. 



