TAXONOMIC MORPHOLOGY 27 



III. Median Mesostebnal Foveae. These foveae also are usually present, 

 but may be widely separated, close together with a common aperture, or fused 

 as one fovea, the median mesostemal fovea. They appear as openings in the 

 mesosternum, just posterior to the prepectoid ridge, and between the usually 

 conspicuous coxal-prepectoid carinae, which run longitudinally on each side 

 of the mesosternum in most species. They penetrate also the prepectoid, in- 

 vaginating anteriorly. In cleared slide mounts they can be easily found when 

 present, but in dry triangle mounts they usually appear as one median fovea, 

 since many species have a common aperture for these foveae. They are shorter 

 than the lateral mesostemal foveae, and in a number of species the lateral 

 and median mesostemals cross each other on each side because of the median 

 course of the former and the anterior course of the latter. 



IV. Lateral Mesocoxal Foveae. These appear as invaginations at the 

 lateral extremity of each mesothoracic coxal cavity. They vary in size from 

 huge invaginations to minute pores; they may lie a short distance from the 

 cavities or be partially lapped by the coxal rim ; they may be nude or pubescent, 

 circular to slit-like, and are present in about sixty per-cent of the species. 

 These lateral mesocoxals are important foveae since they invaginate at a 

 topographic area where a number of sclerites, or sclerotic regions, meet, e.g. 

 mesosternum, mesoepistemum, mesoepimeron, metaepisternum and metaster- 

 num. Three or more of these regions are usually involved in the formation of 

 the fovea on each side, so that each fovea appears as the hub of a wheel with 

 the sclerotic regions radiating spoke-wise from its cavity. Again, examination 

 of cleared slide mounts, in which one mesothoracic coxa has been removed to 

 show the coxal cavity, usually shows the fovea as a deep, conical, segmentally- 

 creased invagination which penetrates anteromedianly below the coxa. The 

 internal, blind end of the foveal lumen continues as a sclerotized fiber which 

 joins the arm of the mesostemal furca of the endoskeleton above each coxa, 

 and passes dorsal to the lateral articulation of the coxa. These foveae, then, 

 are important topographically and appear also to have a direct connection 

 with the endoskeleton (e.g. Tmesiphorus costalis), as was shown also for the 

 vertexal foveae. 



V. Posterior Mesocoxal Foveae. These invaginations may or may not 

 be present. When they occur they should be looked for as a pair of openings 

 along the posterior margin of the coxae, one on each coxal border. The po- 

 sition of these foveae varies considerably. They may be approximate, in which 

 case they lie near the median end of the coxal cavity of each side and their 

 course is anterior into the heavily sclerotized metasternal process or lamina 

 between the coxae; or they may be widely separated, each appearing as an 

 invagination of the posterior coxal border of the metasternum near the lateral 

 mesocoxals noted above ; or they may occupy some intermediate position along 

 the posterior coxal margin. 



VI. Median Metasternal Foveae or Fovea. These foveae are almost 

 always fused as one fovea which forms an invagination in the metasternal 



