420 MR. A. G. BUTLER ON THE GENUS ACROSOMA. [Apr. 1, A List of the Spiders of the Genus Acrosoma, with Descriptions of new Species. By Arthur G. Butler, F.L.S., F.Z.S., &c. [Eeceived March 6, 1873.] In the present paper I have made a complete list of the species hitherto described of this truly remarkable genus : five new species are added, one or two of them being most extraordinary forms. The spines on the members of this group are doubtless protective, either, as (probably) in the case of the Gasteracanth.ee, to render them like the thorny leaves, knots of shrubs, acacias, &c, or, as (probably) in the present genus, to render them unpalatable morsels for insectivorous birds and reptiles. It is a fact, Mr. Bates says, that the Acrosomata spin their webs in the most exposed situations, where they are sure to be seen by any passing enemy. Genus Acrosoma, Perty. 1. Acrosoma cyanospinum. Epeira cyanospina, Lucas, Diet. Pitt. d'Hist. Nat. iii. p. 70, pi. NO. f. 3(1835). Plectana cyanospina, Walckenaer, Apt. ii. p. 178. n.4-2 ( 1837). British Guiana (Schomburyh) ; Rio Negro (Wallace) ; Para (Bates), B.M. We have a variety from Para in which the four anterior spines are red. 2. Acrosoma furcatum. Aranea armata, Olivier, Enc. Meth. iv. p. 205. n. 24. Aranea taurus, Fabricius, Ent. Syst. ii. p. 424. n. 64. Plectana furcata, Walckenaer, Apt. ii. p. 176. n. 40 (1837). Haiti. Seems allied to P. cyanospina. 3. Acrosoma macracanthum. Plectana macracantha, Walckenaer, Apt. ii. p. 183. n. 52 (1837-39). Acrosoma spinosum, Koch (nee Linn.), Arachn. iii. p. 50, pi. 92. f. 210(1836). Para (Bates) ; Brazil (Doubleday). B.M. 4. Acrosoma defensum, n. sp. Cephalothorax elongate, broadly expanded in the centre, with median transverse depression as in A. macracantha : abdomen longi-tudinally subovate, deeply excavated in front and truncated behind, with ten acute spines : — two vertical, rather short at base, springing from either side of the sinus ; two on a prominent transverse ridge, at about one third the length of the abdomen from the base, longer,
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