Prof. S. J. Sltand — Saturation in Petrograi^lty . 485 



inner psiir being on a slightly higher plane, one near liind angle 

 of each eye. Anteiinoe nine-jointed, the breadth of the first four 

 joints, which are finely ringed, being noticeably greater than any 

 of the succeeding and 2-4 sub-equal; joints 5—7 fusiform and 

 apparently sub-equal in length. 



Prothorax transverse, nearly twice as broad across posterior third 

 as long through mi<]dle ; anterior angles obtuse, the hind angles 

 broadly rounded. Surface, anteriorly at least, faintly transversely 

 striate. Each hind angle furnished with two long bristles, about 

 0'6 the length of the prothotax ; a mid-lateral pair backwardly (and 

 sliglitly inwardly) directed and about 0'45 the length of the prothorax. 

 A series of at least two pairs of postero-marginal setae. 



Pterothorax well developed, much broader than prothorax but not 

 quite as broad as the abdomen at broadest. Wings long, about ten 

 times as long as broad near middle, reaching to about the middle 

 of the tenth abdominal segment, apically somewhat pointed ; two 

 distinct longitudinal veins running for the entire length of fore- 

 wing, apparently connected by a cross-vein at about the basal third, 

 and each uniting with the ring-vein near tip. Costa and longitudinal 

 veins uniformly set with moderately long stout setae, the costa with 

 approximately 45, upper vein 23, and the lower vein 18 ; a single 

 seta set near apex of wing, just beyond fore-vein but not on it. 

 Setae as long as or longer tlian 0-35, the breadth of wing near middle. 



Abdomen — excluding segment 10 — elongate - ovate, the ninth 

 segment narrowing to base of 10, Avhich latter is exceptionally 

 elongated, a little longer than the length of tlie head and prothorax 

 together; ventrally open for its entire length and furnished with 

 a series of setae just before apex. Ninth segment furnished with 

 four postero-marginal bristles, of which the outer pair is apparently 

 longer than tlie inner and about 0-5 the lengtli of the tenth segment ; 

 also furnished with another and shorter dorsal, dorso-lateral, or 

 lateral pair on a higher plane. 



EXPLANATION OF PLATE XXXVI. 

 Fig. 1. Stenuyothrips sitccinexis, gen. et sp. nov. x 35. 



,,2. ,, ,, Head and prothorax. X c. 70. 



,,3. ,, ,, Ninth and tenth abdominal segments. x70. 



,, 4. ,, ,, Underside of tip of tenth abdominal segment. 



x 70. 

 ,, 5. ,, ,, Right fore-wing. X c. 50. 



Formation and locality : from Tertiary Lignite Deposits, shores of the 

 Baltic, extending from Dantzig to Memel, etc. 



III. — The PiuNCiPLK oi- Saturation in Peti;0(;IKai'HY. 



By S. J. Shand, D.Sc, F.G.S., 

 Professor of Geology, Victoria College, Stellenbosch, South Africa. 



IN a recent number of this journal' I advocated the systematic 

 employment of a certain criterion in connexion with the 

 classification and nomenclature of igneous rocks, that criterion being 

 the ' saturated ' or ' unsaturated ' character of the minerals constituting 



1 Geol. Mag., November, 1913, pp. 508-14. 



