ACARIDA 



absolute certainty cannot be attained without breeding them, but I shall hère treat the Acarus 

 as a nymph, not as a separate species. 



Form very similar to that of the adult, but less widened posteriorly. Céphalothorax 

 and abdomen separated by an almost straight Une ; the latter considerably higher in level 

 than the former. Color dark brown, very dark for a nymph ; but not so dark as that of 

 the adult, rather yellower. Céphalothorax broad ; marked with numerous irregular ridges, 

 especially near its base where there are two pyramids of small converging ridges which 

 support a larger W-shaped ridge the antero-lateral ends of which nearly touch the pseudo- 

 stigmata. Pseudo-stigmatic organs and interlamellar hairs like those of the adult. Legs somewhat 

 shorter than those of the adult, chiefiy in conséquence of the shorter tibiae, otherwise very 

 similar in form ; rough on the outer side : claw large and monodactyle. Abdomen thick, 

 slightly arched. Notogaster covered with irregular, vermiform and other ridges ; thèse are 

 small, closely crowded, and more or less transverse on the central part of the abdomen ; 

 toward the latéral and posterior portions the notogaster is covered with larger, rather straighter 

 ridges which leave large irregular pits between them ; the larger ridges are chiefiy almost 

 longitudinal ; but are mostly transversely marked with short portions of the smaller ridges. 

 There are a few very short, fine hairs on the notogaster ; chiefiy toward the edges. The 

 vermiform ridges continue on the side of the abdomen. Ventral surface much smoother than 

 the dorsal. 



Notaspis Belgicae sp. n. 



Average length, about o mm ,56. 



Average breadth, about o mm ,32. 



This species is of the same character as N. antarctica, but much smaller and with 

 numerous spécifie différences. 



Form elliptical, but pointed anteriorly and having a tendency to be pointed poste- 

 riorly also. 



Color chestnut-brown (castaneus), moderately dark. 



Texture dull, very slightly rough. 



Céphalothorax conical, without markings; rostrum pointed. The posterior part has a 

 flattened expansion on each side which is slightly excavated for the insertion of the first 

 and second pairs of legs. Mandibles powerful, tridentate; the terminal tooth of the moveable 

 arm of the chela is the longest. Lamella? almost obsolète ; they are ridges so little raised 

 as to be easily overlooked. Rostral hairs near together, thick, slightly clavate. Interlamellar 

 hairs very long, near together, quite perpendicular, straight, stiff, rough, dark. Lamellar 

 hairs much shorter, almost similar in character but strongly serrated. Pseudo-stigmata incon- 

 spicuous, slightly anterior to a transverse line drawn through the interlamellar hairs. Pseudo- 

 stigmatic organs with very small, pyriform, almost globular heads on very short peduncles. 



Legs of moderate length ; the genuals of the first pair about reach the point of the 

 rostrum ; the femora are the longest joints and are somewhat flattened. The hairs, except 

 those on the tarsi and the tactile hairs, are thick and mostly curved, some are slightly clavate ; 

 there are two on the inner and one on the outer side of each fémur of the first two pairs, 

 one pair on each genual, and a few on the other joints. Hairs on the tarsi numerous, setiform, 

 flexible. Claws tridactyle, very heterodactyle. 



