TEMNOPLEURID^. 293 



test is not sculptured (with rare exceptions) but along the horizontal sutures or 

 at the angles of the plates in the median line of each area are found deep pits, 

 the form and size of which are very variable. They may be so large as to furnish 

 the most conspicuous character of the test or they may be so small as to be ea-sily 

 overlooked, and they may be practically wanting in old specimens. In addition 

 to these pits, the Temnopleurinae have another characteristic feature in the 

 union of the coronal plates by dowelling. No very extensive study of this 

 feature has been made to determine its significance or its relation to youth and 

 maturity. While it may be of more morphological importance than seems hkely, 

 it is so difficult a feature to detect that it is of Httle practical importance in 

 distinguishing species and genera. 



Aside from the structure of the corona, the character of the abactinal system, 

 the condition of the buccal membrane, and the arrangement of the buccal plates 

 all furnish characters of importance in classification. It is rather remarkable 

 that while the abactinal system of the Temnopleuridse retains, with few exceptions, 

 the primitive character of having all the ocular plates small and broadly exsert, 

 the actinostomal membrane is with few exceptions thin and bare and even 

 the buccal plates may show indications of resorption or the buccal tube-feet be 

 reduced to five. The crenulation of the primary tubercles is a matter of some 

 importance in this family as it furnishes the most obvious character for dis- 

 tinguishing certain genera. The arrangement of the pore-pairs is of no httle 

 importance in distinguishing some species of the more highly specialized genera, 

 and the number of coronal plates is frequently of value as a character. Size 

 and color are often of very great significance and certain species are only to be 

 distinguished by some characteristic feature of their coloration. As a rule the 

 genera are not difficult to distinguish, if reasonable care is used, but in certain 

 genera, notably Prionechinus and Amblypneustes, the separation of the species 

 is very difficult and the results are not always satisfactory. The following table 

 shows those characters which have proved of most use and reliability in arranging 

 the forty-five species, which have been personally examined, all of the sixtcei^ 

 genera except Lamprechinus being represented. 



Test without pits on sutures or at angles of coronal plates, but more or less exten- 

 sively ornamented with grooves, depressions, ridges or knobs; coronal plates 



not united by dowelling Trigoxocidarin^. 



Sculpturing of test, when well marked, consists of vertical or diagonal ridges, 

 usually connecting tubercles, but it may be so faint as to show little 

 character; it is sometimes best marked on abactinal system. 

 Actinostomal membrane fully plated; buccal plates not conspicuous 

 among the others. 



