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Show 284 DR. n. GADOW ON EVOLUTION [Mar. 20, total of these and of many others produces that general something which so often tells the experienced what kind of lizard he has Text-fig. 65. Lepidosis of the collar and throat. A=C. immutabilis, Salina Cruz No. 1. Edge of collar formed by a complete row of granules. A nest or cluster of enlarged granules in the centre of the throat. • B = C . mexicanus, var. balsas No. 8. Collar composed entirely of very large scales. C=C. deppei from San Carlos. A few single granules intercalated between the large scales forming the edge of the collar. 1)=C. sexlineatus from North Carolina. E = C deppei, Cocoyul No. 5. ¥=C. communis australis, Cuicatlan, half-grown. Collar composed of very small scales and many granules. got hold of, before submitting it to his artificial keys, which really interesting cases often refuse to work. Supraoculars + Collar + Humerus + Forearm -f- Femur -f Pores + Coloration = Species, is a kind of condensed equation, but the line has to be drawn at its length, lest the equation becomes bewildering when comparing the variations of many kinds with each other. Since each of these characters may have at least two values (large or small in numbers or in size as the case may be), the possible number of |