1902.] ON THE SPIDERS OF THE GENUS LATRODECTUS. 247 



senting the type of an highly-organized reptile, and nearer to the 

 Dinosaurs than any other living type. As in the genus Testudo, 

 the right auriculo- ventricular valve of the Birds is almost always 

 a clearly-defined and semi-lunar muscular flap, practically guarding 

 only one side of the auriculo- ventricular orifice. In Testudo, as in 

 the bird, the opposite side of the ventricle has a perfectly smooth 

 surface, without even the rudiment of a ridge to correspond to the 

 valve which lies on the left side of the auriculo -ventricular 

 orifice. On the other hand, the left auriculo- ventricular aperture 

 is guarded by a completely, or nearly completely, encircling valve 

 in both tortoise and bird. Hardly any change is required to 

 convert the right auriculo- ventricular valve of the tortoise into 

 that of the bird. If no rudiments, such as those described in the 

 present communication, of a septal half to the right auriculo- 

 ventricular valve had been discovered, it might be reasonable to 

 dwell upon the striking but really superficial likeness which this 

 valve in the vast majoiity of existing birds shows to the corre- 

 sponding valve in the tortoise. But it seems now to be clear 

 that the simple valve in the bird's right ventricle is not the 

 persistent and simple valve of the toi-toise or some lower 

 reptilian type ; but that it has been derived from the reduction 

 of a more complicated valve such as is possessed by the Crocodiles, 

 and was very possibly possessed by the Dinosaui-s. The evidence 

 is therefore so far in favour of assigning to the birds an origin 

 from some highly-developed reptilian type. 



2. On the Spiders of the Genus Latrodectus, Walckenaer. 

 By Frederick Pickard Cambridge, F.Z.S. 



[Received February 25, 1902.] 

 (Plates XXYI. & XXYII.^) 



Contents. 

 I. Introduction, p. 247. 

 II. List of Species and Sub-species recognized in this paper, p. 252. 



III. Alphabetical List of Species described or figured, p. 256. 



IV. Explanation of the Plates, p. 261. 



I. Introduction. 



The genus Latrodectus of Walckenaer (Tableau, p. 81, 1805), 

 of which the type is L. A-tredecim-guttatus (Rossi), 1790, com- 

 prises those very interesting Spiders which, under various local 

 names, have been notorious in all ages and in all regions of the 

 World where they occur on account of the reputed deadly nature 

 of their bite. 



As to the evidence, there can be no doubt whatevei- that the 

 inhabitants of those regions sufier frequently from blood-poisoning 



1 For explanation of the Plates, see p. 261, 



