542 Mr. D. Sharp and Mr. F. Muir on the Comparative 
Family LYMEXYLONIDAE. 
Forms examined: Afractocerus valdiviensis? Ph., Chile. 
A. africanus Boh., Madagascar. 
Figs. 149 and 150 Pl. LXVI. 
Atractocerus valdiviensis? (Pl. LXVI fig. 149). 
Median lobe short and bulbous, drawn out to a short point at 
apex where the median orifice is situate, base produced into two 
short median struts; median foramen at base. Tegmen forming a 
shallow concavity in which the median lobe rests, and consisting of 
two sclerites; a distal bilobed (lateral lobes) piece, with two struts 
encircling the median lobe and a curved basal-piece connected to 
the lateral lobes by a membrane (em 1). The internal sac appears 
to be simple, which is exceptional when the median lobe is bulbous. 
We speak with much hesitation as to this and the following 
owing to the bad preservation of the two individuals. The speci- 
mens of this genus are too often found to be in a disastrous state in 
collections. 
Atractocerus africanus (Pl. LXVI, figs. 150, 1507), 
Median lobe long and slender with orifice at apex and foramen at 
base, Lateral lobes complex, forming a pair of large complex lobes 
joined together on the ventral aspect where they form a medial square 
plate (a) deeply emarginate in the middle, and on the dorsal face 
continue as two flat sclerites which join together at their bases where 
the median lobes articulate (pa). The basal-piece forms a large shield- 
shaped plate on the ventral face, the distal corners prolonged into a 
pair of obtusely rounded projections, Internal sac undifferentiated. 
The anus of this species opens at the end of a large tube, which 
lies over the aedeagus. 
These two types differ from one another and do not 
approach to any of the other trilobe forms. We anticipate 
that they will prove to be of important bearing. 
Family DASCILLIDAE. 
Forms examined: Ptilodactyla sp., Brazil. Dascillus 
cervinus L., England. 
Figs. 151 and 152 Pl. LXVI. 
Ptilodactyla (not named in Brit. Mus.) (Pl. LX VI fig. 151). 
A trilobe form. Median lobe well developed, tapering to a fine 
point at apex ; median orifice on ventral aspect, forming a long slit 
