part 2] sviuxGOTiiYius axi> situiieuixa. 197 



represented a continuous juguni such as is present in Spiri- 

 ferina, or mere jugal processes like those of, for instance, Spirifer 

 striatal 



On the classification given in the second English edition of 

 Zittel's ' Palaeontology,' Tylothyris would appear to belong to the 

 sub-family Trigonotretinse, Schuchert ; it certainly does not belong- 

 to the family Suessiidre, which includes Spiriferina. 



TrLOTHYRis LAftiorosA (M'Cov) emend. (Text-figs, lm, 1//, 4^, 

 & 4 6, pp. 166, 199 ; PI. XIII, figs. 1, 2, 12, 13, & 16.) 



18-14. Cyrtia laminosa M'Cov [20 j p. 137 & pi. xxi, tig. 4. 



1844. Spin/era decemcostata M'Coy, op. cit. p. 131 &'pl. xxii, fig. 9. 



184-1. Spirifera mesogonia M'Coy. op. cit. p. 137 & pi. xxii, tig. 13. 



1855. Spirifera laminosa M'Coy [21] p. 426. 



1887. Spiriferina laminosa De Koninck, Ann. Mus. Roy. Nat. Hist, lielg. 



vol. xiv, pt. 6, pp. 103-105. 

 1905. Syringothyris att'. laminosa Vaughan, ' Bristol Paper ' [33] p. 300. 

 1911. Syringothyris laminosa (auctt.) Vaughan, ' Barrington Paper' [28 J p. 383 



& pi. xxxi, tig. 8. 



Description. — Shell spiriferoid, of medium size, about twice 

 as wide as long ; greatest width along the hinge-line. 



Pedicle- valve sub-pyramidal, cardinal area rather more than 

 three times as wide as high, concave, nearly fiat in the neighbour- 

 hood of the hinge-line, but with increasing curvature towards the 

 beak, which is very slightly incurved ; apical angle about 120°. The 

 beak of the pedicle-valve lies considerably above a line perpendicular 

 to the plane of the brachial valve (see text-figs. 4« & 4<b, p. 199). 

 Delthyrium nearly twice as wide as high, delthyrial angle about 35°. 

 Delthyrial covering unknown. Lateral slopes evenly convex; mesial 

 sinus wide, subangular, and terminating in a rounded wave at the 

 anterior margin of the valve. A line along the floor of the sinus 

 from the beak to the anterior margin is evenly curved. 



Brachial valve convex, the greatest convexity being in the 

 neighbourhood of the beak. Mesial fold narrow at its commence- 

 ment, but increasing rather rapidly in width toAvards the anterior 

 margin, where it is considerably raised above the general level of 

 the valve. 



Each lateral slope in both valves is ornamented by ten or twelve 

 simple costa? decreasing gradually in size towards the cardinal 

 extremities ; the last four or five costas are short and inconspicuous. 

 They are subangular, and are separated by deep furrows, each 

 about as wide as the costa? on each side of it. 



Surface of both valves, except the cardinal area of the pedicle- 

 valve, crossed by well-defined, regular, imbricating lamelhe of 

 growth, which are, on the average, about half a millimetre apart. 

 Shell-structure foliaceous, fibrous, and impunctate. 



Internal structures: — Pedicle - valve. — The delthyrial 



1 The jug'iim is the transverse shelly band and its accessory processes which 

 iinite the primary lamellfe of the spiralia. If the band is incomplete, its parts 

 are known as ' jugal processes.' 



