SINUITES PSEUDOCOMPRESSUS. 11 



Horizon. — Lower Ortloviciaii : Balclatchie Group. 



Localities. — Ardinillan ; Balclatchie (r), Girvan. 



Bemarhs. — The shape aucl cross-section of the shell resemble f>. soiverhyi, 

 Perner/ but the angulatecl apertural lobes are similar to those in *S'. recta iignldvis 

 (Ulr. and Scof.).^ From 8. halclatchiensis it differs in shape, the more rapid increase 

 in height of the whorls, the broader sinus, and angulated apertural lobes and pair of 

 marginal internal thickenings. Similar internal transverse ridges are met with 

 in 8. obesus (Ulrich) ^ from the Ordovician of America and in " Bellerophon " 

 strangulatus, Barrande,'^ as well as in De Verneuil's " Bellerophon hilobatns " from 

 Spain ^ and Eichwald's Belleropliou navicida ^ from the Lyckholm Beds of Dago. 

 Many of the British species described in this memoir possess such thickenings. 



This species is dedicated to Dr. Alexander MacCallum, who was one of the 

 earliest geologists to pay attention to the Girvan area. 



The types are in Mrs. Gray's Collection. 



8. Sinuites pseudocompressus, sp. nov. PI. II, figs. G — 8. 



1852. Belleroplion bllobatus, Sowerby, McCoy (pars), Syn. Brit. Pala30z. Foss. Woodw. Mus., fasc. ii, 

 p. 308. 



8pecific Characters. — Shell compressed, rounded ; back narrowly rounded, sides 

 somewhat flattened ; umbilicus closed or very small, situated at about one-third 

 the height of the shell. Outer whorl increasing rapidly in height to mouth. 

 Mouth higher than wide, widest at base, semi-oval to parabolic, with large sub- 

 angular lateral lobes projecting forwards, and large deep, blunt, V-shaped sinus in 

 outer lip; base of lip slightly reflexed at umbilicus. Surface of lateral lobes 

 marked with fine lines parallel and close to edge of lip ; rest of surface of shell 

 smooth?. Interior of shell with weak, broad, rounded, transverse internal 

 thickening forming a rounded band running up from umbilicus with slight 

 sigmoidal curve and touching base of sinus on dorsum. Occasionally traces of 

 similar but weaker posterior transverse narrow internal thickenings are present 

 near the umbilicus and on the sides of the outer whorl at about half to three- 

 fourths the height of shell. 



iZorizoM.— Middle Bala. 



Localities. — Cheney Longville ; Horderley. 



^ Peruer, o^j cit., p. 61, pi. Ixxxvi, figs. 27 — 32, text-figs. 28 — 36. 

 ^ Ulrich and Scofield, o]j. cit., p. 868, pi. Ixiii, figs. 15 — 20. 

 3 Ibid., p. 874, pi. Ixiii, figs. 45—47. 

 * Perner, o^. cit., p. 159, pi. Ixxxvii, figs. 12 — 14. 



3 De Verueuil, ' Bull. Soc. Gcol France,' [2] vol. xii, 1855, p. 984, pi. xxvii, fig. 1. 

 6 Eichwald, ' Urwelt Russlands,' pt. 2 (1840), p, 57, pi. iii, fig. 3 ; Kokeu, ' Gastrop, Bait. 

 Untersilurs,' p. 120. 



