130 INSECUTOR INSCITI^ MENSTRUUS 



the button appear to be absent. The cephalopharyngeal skele- 

 ton shows well in numerous specimens as a V-like mark with 

 the hypostomal sclerite wedged in the base of the V. The de- 

 tails can not be made out satisfactorily, owing to the pressure 

 that has been exerted on the skeleton, massing the sclerites to- 

 gether and distorting or obscuring their outlines. The pharyn- 

 geal sclerites are well elongated, and the hypostomal heavy. 

 The two mandibular sclerites appear to be elongate, sharp, and 

 nearly straight. 



The pupa is distinguished from that of Hypoderma by the 

 strongly tuberculate lateral borders, as photographed and fig- 

 ured by Cockerell. 



The examination of the shales in the National Museum col- 

 lection shows that anal stigmatal plates and cephalopharyngeal 

 skeletons are numerously represented and scattered in various 

 places among the remains. There are a few excellently pre- 

 served specimens of nearly the whole maggot. In at least two 

 specimens of the latter, one being both figured (fig. 4) and 

 photographed (fig. 6) by Cockerell, the two main trachea] 

 trunks can be very clearly seen, and even the deli- 

 cate spirals of chitin which supported the tracheal 

 walls in life are plainly visible and perfectly preserved. In 

 numerous cases the chitin of the maggot integument and pupa- 

 rium is preserved in the shales unchanged since the Eocene, 

 during the lapse of a period of time probably not less than two 

 million years. 



It seems safe to assume that Lithohypo derma was a sub- 

 cutaneous bot of some North American Eocene bovine, most 

 probably the ancient progenitor of the modern bison. The 

 large numbers in which the bots occur in the shales is easily 

 explained by their dropping from the host at places where the 

 latter congregated to water. 



