PETRUNKEVITCH, AMERICAN SPIDERS 
209 
and so brilliant that the first impression is that of a coral red spider. Its 
local name is “ aragna Colorado,.” Instead of living under rocks as in Ja¬ 
maica, it makes its webs some six feet above the ground among the branches 
of the cactus, where it often hangs with several males. As many as eight 
males, indeed, were found in one web. And yet no structural difference can 
be found between this “red spider” and the “black widow” of the southern 
United States. The L. insularis Dahl with its two varieties becomes there¬ 
fore a synonym of mactans. 
Theridionexus gen. nov. 
Cephalothorax humilis, impressione transversa recta notata; oculorum linea 
antica recurva, postica levissime procurva; oculi inter se fere £equidistantes, medii 
antici reliquis minores, nigri; laterales eontigui; quadrangulus antice quam postice 
angustior, postice latior quam longior; clypeus quadrangulo multo latior; chelae 
sat longae, pro margine (superiore) obliquo tridentato, retroma' gine (inferiore) muti- 
co; pars labialis latior quam longior, dimidium laminarum non attingens; laminae 
subrectae; sternum triquetrum, antice truncatum, postice acuminatum; pedes longi, 
mutici; tarsi unguibus spuriis 2-2 muniti, ungues superiores geniculati, pectinati; 
unguis inferior muticus; tarsi postici pectine muniti; abdomen globosum, organo 
stridulante carens. 
Typus: T. cavernicolns. 
6. Theridionexus cavernicolus sp. nov. 
Plate XXI, Figs. 6, 7. Plate XXII, Figs. 30, 31, 32, 33, 34, 37. 
The spider for which I propose the new genus combines the characters 
of two families. Its general appearance, the long front legs and the globose 
abdomen and most of all the presence of a well developed tarsal comb speak 
for its close relation to the family Theridiidse. On the other hand, the 
structure of the mandibles, the shape of the cephalothorax and especially 
the presence of a tibial apophysis in the male palpus are characters which 
are found only in Argiopidae. It is, therefore, impossible to place the genus 
Theridionexus with sufficient reason in either of these families; it forms a 
new, intermediate group. The proposed name expresses to a certain degree 
the affinities of the genus. 
Female.— Cephalothorax, 2.7 long, 2.1 broad between second and third pair of 
legs; abdomen, 4.0 long; legs in order 1243. 
Legs 
Femur 
Pat. 4- Tib. 
Metatar. 
Tarsus 
Total 
I 
7.1 
7.9 
6.8 
2.6 
24.4 
II 
5.3 
5.7 
4.7 
2.0 
17.7 
III 
3.2 
3.1 
2.8 
1.3 
10.4 
IV 
5.0 
4.6 
4.0 
1.6 
15.2 
