46 
Psyche 
[June 
» J lOOfj. 
Fig. 1 A, B — Beorn leggi Cooper; C, D. — juvenile heterotardigrade (an 
echiniscoid?). Compare these camera lucida sketches with the photographs of 
plate 6. Scale represents 100 microns. 
P — “head”; I, II, III, IV — body segments bearing legs; a, p — anterior 
and posterior halves of segments I, II, etc., each marked off by a dorsal 
furrow; IVa = “pseudosegmental region” of others; s — apical cuticular 
projection or spine; 1 + 2 — “inner” pair of claws, of which 2 is the dorsal 
element; 3 + 4 — “outer” pair of claws, of which 3 is the dorsal element; 
claw 2]>3>1>4, see text. Dotted lines represent wrinkles and depressions. 
skeletal elements, presence or absence of cloaca, or gonopore and anus, 
or indeed whether there are 4 claws per leg or 2 two-rayed claws, 
Beorn can nonetheless be given ordinal assignment. Though this 
must be done chiefly by the negative process of exclusion, the absence 
of cephalic appendages, of a lateral cirrus, and of a clava, are sufficient 
to eliminate assignment to either the Mesotardigrada (1 genus ; Rahm 
1937) or to the Heterotardigrada (4 families, ca. 10 genera, see 
Marcus 1929, 1936). The remaining order, Eutardigrada, encom- 
passes but two recognized families: Milnesiidae ( — Arctiscidae; 1 
genus : Milnesium) and Macrobiotidae (4 genera : Macrobiotus, 
Hypsibius, Itaquascon, and H aplomacrobiotus) . The obvious lack 
of rostral and lateral palps, no less the morphology of the claws 
