530 Mr. D. Sharp and Mr. F. Muir on the Comjmrafivc 



Family BYRRHIDAE. 

 Form examined : Byrrhus gigas Fabr., Alps. 



B. gigcis. 



Of the simple trilobe type. Median lobe cliitinoiis along the 

 dorsal aspect, the apex of which is cleft, eacli point flattened and 

 slightly twisted ; struts at base very short ; median orifice 

 supported by a very attenuated chitinous ring, the ventral 

 margin prolonged into a sharp-pointed lobe, supported on the ventral 

 face by a narrow chitin plate. Lateral lobes well developed, their 

 bases meeting on dorsal and ventral aspects, and thus enveloping the 

 median lobe, their apices pointed ; point of articulation on the dorsal 

 aspect. Basal-piece triangular. Internal sac undifferentiated. 



This is very like Hgdrophihis. 



Family CHELONARIIDAE. 



Form examined : Chelonarium zapotense Sharp, Guate- 

 mala, and C. errans Sh. 



Chelonarium zapotense (PI. LXII figs. 122, 122«). 



This is a highly specialised trilobe form. Median lobe short, stout, 

 highly chitinised ; the ventral side being drawn out into two long 

 median struts. To the ends of these struts is articulated a median 

 process, bilobed at the base, slender in the middle an-d divided into 

 two long, slender, flat, bent, distal processes (n). Lateral lobes small, 

 rounded at apex and curved. Basal-piece formed by a large sclerite 

 on the ventral aspect, with lateral and basal edges curved up; 

 dorsal side membranous. Internal sac undifferentiated. 



C. errans is exactly the same type, but some details are different 

 (i. €. the slender process (a) from the ventral aspect is single). 



Family CYATHOCERIDAE. 



Form examined : Cyathocerus horni Sh., Central America. 

 Figs. 123 and 123a PI. LXII. 



C. horni (PI. XLII figs. 123, 123«). 



Median lobe long, thin and crooked, with median orifice at apex 

 and median foramen at base on dorsal aspect. Tegmen forming 

 sheath with the distal end cleft along the dorsal aspect, but with- 

 out division between lateral lobes and basal-piece. Internal sac 

 undiflferentiated. 



