96 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvi. 



at each angle and a pair on each of the transverse margins, and in 

 some species one in the middle of each side. The maximum number 

 is therefore twelve. When onlv one or two pairs are present they 

 are at the hind angles. The form and size of these spines is also varia- 

 ble. They may be quite short and inconspicuous or nearly as long as 

 the protonum itself. In many Plceothripidje they are knobbed or 

 funnel shaped at the tips. 



In a number of species of Tubulifera, a division of the pronotum 

 into plates near the hind angles has been observed. Two triangular 

 plates coming up from l)ehind the middle on the side and at about the 

 hind angles meet at a point considerably within the margin and above 

 the fore coxa?. The prosternum is less strongly chitinized than the 

 pronotum and at about the middle of the fore edge is often indented 

 to accommodate the mouth cone. The insertions of the fore coxse are 

 at the hind angles and the distance between them depends upon the 

 width of the hind edge of the prothorax. In some species the proster- 

 num appears to be entirely membranous, while in others there are two 

 small plates between the coxte near the hind margin. The episternum 

 and epimeron arc more easily distinguishable in most Tubulifera than 

 in Terehrantia. 



2fesothorax. — The mesothorax is a broad, short segment, often the 

 broadest of the body. The mesonotum is shorter than the mesosternum, 

 though the latter approximatel}^ equals the metasternum as a rule, in 

 consequence of which the division between the meso and metathoracic 

 segments is oblique. The mesoscutum is usually a rather hexagonal 

 plate, somewhat broader than long, and has thickened edges which are 

 bent inward and used for the attachment of muscles, as is shown by 

 cross sections of this region of the l)ody. A narrow prescutum can 

 be easily distinguished in some species, though in others it appears to 

 be closely fused with the scutum. On each -side of the scutum is a 

 membranous area upon which the fore wings are inserted, at the 

 bases of which there are chitinous thickenings for the attachment of 

 muscles and also serving as pivotal points. A small, curved, triangular 

 tegula is present in many, if not all, Terebrantia. Upon its ])road 

 edge, next the base of the wing, it is furnished, in ^^olothrips, with 

 a row of five or six small, stout spines which point directly toward 

 the base of the wing, upon which, very near its base, there stands a 

 somewhat larger, curved spine which, when the wings are extended 

 in flight, points toward and would appear to engage some one of those 

 upon the tegula. This is a peculiar and interesting structure the 

 purpose of which can only be conjectured. In Thripida^ the tegida is 

 present, but I have found no species having the spines fully developed, 

 though little knobs or vestiges of such structures are present in some 

 cases. The tegula is not always distinctly visible. At each anterior 

 angle of the mesothorax there is a larger or smaller spiracle, which is 



