18 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. G4. 



Tenth abdominal segment, terminal, cylindrical, almost as long as 

 ninth, one-third narrower; anterior half slightly chitinized, and 

 po'iterior half membranous with round anal opening. 



Spiracles, annular ; one thoracic and eight abdominal pairs. The 

 thoracic spiracle, in the mesothoracic preepipleurum, about as large 

 as tibia in cross section. The first seven abdominal spiracles placed 

 in the middle of the ventral surface of the lateral expansions of the 

 tergal shields. The eighth abdominal spiracle on top of the spiracle 

 bearing hook. The first abdominal spiracle as large as the thoracic 

 one; the rest much smaller and rather minute (fig. 1). 



Spinning glands on ninth or tenth abdominal segments not found, 

 but microtomical sections have not been made ; the first instar, how- 

 ever, has been observed by the present writers (see p. 6) to spin a 

 thread, lowering itself with head turned downward, but it was not 

 definitely determined from what part of the body the thread origi- 

 nated; possibly it is an exudation from the malpighian tubules and 

 comes out through the anus. 



Differentiating characters. — The genus Tricrania belongs to the 

 subfamily Nemognathinae^ as borne out by the biological and morpho- 

 logical characters of both imago and the six larval instars. The 

 first instar of this subfamily is always carried by a bee-host to its 

 nest. It has spiracle-bearing elevations on the dorsal side of the 

 eighth abdominal segment, a head with labrum, clypeus and frons 

 fused together, two ocelli on each side and dentate mandibles which 

 move in a plane ti-ansverse and vertical to the body ; tarsus, as a rule, 

 is conicofalcate and ninth abdominal segment has either two fine 

 and short caudal setae, or none. 



In this subfamily the first instar of genus Homia is distinguished 

 by mandibles with seven or eight teeth ; Homia minutipennis, also by 

 low, rather soft spiracle-bearing elevations on eighth abdominal 

 segment. First instar of Stenoiia has spathulate tarsus and both 

 tarsal setae almost as long as tarsus itself; it approaches Tiicrania 

 closely by possessing six teeth on the mandible, all the rest of the 

 genera of the Nemognathinae having but two or three teeth. Sitaris 

 and Apalus have fine and short tarsal setae. Nemognatha, Zonitis, 

 Leptopalpus^ and Sitarohrachys which are well limited from all the 

 other genera by having the sixth instar adherent to the exuvium of 

 the fifth instar are not easily characterized as a group by their first 

 instars. In Nem&gnatha first instar is without caudal setae, the 

 medio-dorsal suture is present on all thoracic segments and continued 

 on the head into the epicranial and frontal sutures, and the tarsal 

 setae are two and almost as long and strong as tarsus. In Zonitis 

 hilineatus the spiracle bearing hooks are short and distant, and 

 this character applies according to Cros' description, also to the 

 genus Leptoeephalus, but in all the old world species of Zonitis, in- 



