NKUROPTERA— THYSANURA— BALLOSTOMA. 101 



which we should in vain seek elsewhere, and the ])roljability that we find 

 here its nearest allies is rendered very strong, and the more so from the 

 diversity of form and type in this group since the addition to it of Scolo- 

 pendrella. The discovery of a coUophbre or something homologous to it 

 would, we conceive, be decisive on the point ; but the lateral preservation 

 of nearly all the specimens of this fossil, and the obscurity of the base of 

 the abdomen in nearly all, not only forbid its determination in those yet 

 found, but render it doubtful if it will ever be discovered. 



The position of this group among the Thysanura must be an independ- 

 ent one between the Cinura and the Symphyla and of an equivalent value 

 to them. For such a group the name of Ballostoma is proposed, in reference 

 to the remarkable power possessed of thrusting forward the gullet and mouth- 

 parts. It would be characterized by the peculiarity named, by the lack of 

 any chitinous frame-work of the head, the equal development of three 

 thoracic segments developed dorsally as shields, and all separated from a 

 cylindrical abdomen, which is armed at tip with a pair of hooks for crawl- 

 ing ; legs largely developed and with expanded and flattened femora and 

 tibiae, the tarsi two-jointed. The principal points towai'd which attention 

 should be directed for the more perfect elucidation of its structure are the 

 buccal plates and a possible collophore. 



Bertkau compares Planocephalus with an insect from the brown coal 

 of Rott, Rhenish Prussia, described by Heyden as a mite under the name 

 Limnochares antiquus. This Bertkau regards as a larval Galgulid, one of 

 the Hemiptera, and he believes Planocephalus something similar ; but he 

 does not seem to me to justify this latter view, and the abundance of Pla- 

 nocephalus with the absence of mature Galgulida; at Florissant seem an 

 obstacle not easily thrown aside. 



Ordinary length when extended, 7-8™'" ; breadth, 2.5-3""° ; diameter, 

 of mouth-parts, 0.5"'". 



Florissant. Sixty-six specimens, of which the best are Nos. 302, 574, 

 3508, 5229, 6933, 7907, 9782, 9896, 10551, 12807. 



