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ROBERT S. BREED AND ELSIE F. BALL. 



the underlying metathoracic groove. When the elytra are sepa- 

 rated, the cross section of the right one appears as in Fig. 2. 

 The ridge b is stiff, but the ridge d, being narrower at h, acts like 

 a spring. When the two elytra are drawn together, the ridge c 

 strikes the ridge d and bends it downward. The ridee c then 



Fig. 2. Cross section of the mid-dorsal portion of the right elytron o{ Lachno- 

 sterna, showing the relation of the two ridges when the two elytra are not locked 

 together. X 75- 



slips into the groove 7, and d springs back, holding c tightly in 

 the groove/. By comparing Fig. 2 (a figure of the right elytron) 

 with that of the left elytron represented in Fig. i, it will be seen 

 that the two are remarkably alike when the elytra are separated. 

 No conception of the way in which they interlock was formed 

 until the two were studied in their natural relations by the method 



Fig. 3. Cross section of the mid-dorsal edge of the left elytron of Lachuosterna 

 as seen in the extreme anterior portion. X75- 



described above. The ridges and grooves along the dorsal suture 

 have essentially the same form throughout the length of the 

 elytra but the joining is the firmest along the anterior third of 

 the suture. Figs. 3 and 4 represent the region close to the point 

 of the scutellum. Figs, i and 2 show the structure at a point 



