474 



THE GEOLOGIST. 



named character is that which generally distinguishes it best from T. hastata 

 and T. vesicidaris ; but, although this pecuHar sinus is well and 4eeply 

 marked in many individuals, it is at times but obscurely seen in others ; and 

 this cii'cumstance has no doubt tempted some palseontologists to unite both 

 Sowerby's and Martin's shells under a single denomination. 



I am acquainted with but few Scottish specimens. It was found by Dr. 

 Flemmg somewhere in West-Lothian ; and Mr. Armstrong collected a few 

 examples at West Broadstone, near Beith, in Ayrshire. 



III. — Teeebratula vesiculaeis. De Koninck. PI. xii., fig. 5. 



Terebrafula vesicularis, De Koninck, Animaux Fossils de la Belgique (SuppL), 

 p. 666, pi. Ivi., fig. 10, 1851. Dav. Mon. Carb., p. 15 ; pi. i., figs. 25, 

 26, 28, 31, 32 ; pi. ii., figs. 1-8. 



This small shell usually presents an ovate or pentagonal shape, is longer 

 than wide, with its greatest breadth near the middle. In some adult examples, 

 and in aU young individuals, the valves are evenly and moderately convex, but 

 after a certain age a smus with two lateral ridges is developed in the dorsal 

 valve ; and at a stiU later period a smaU central elevation or rib is produced 

 towards the front, forming a somewhat W-shaped frontal wave, of which the 

 angles would be rounded. The ventral, or larger valve, is deeper and more 

 inflated than the opposite one ; the beak rounded and incurved ; foramen small, 

 and partly surrounded and separated from the hinge-line by a smaU. deltidium ; 

 surface smooth. The internal dispositions are quite similar to those of 

 T. limtata and T. sacculus. T. vesicularis is a small shell, and may be distin- 

 guished from the last-named species by the small mesial rib in the dorsal valve. 



I am acquainted with but one or two examples which were found some- 

 where in West-Lothian by the late Dr. Fleming. 



[NOTA. — The three species of Terebratula above described are all with which I am 

 acquainted from the Carboniferous rocks of Scotland. At page 17 of my "Monograph," 

 published by the Palaeontogi^aphical Society, I mentioned that Dr. Fleming possessed a Tere- 

 bratula from West-Lothian, which I thought might be referred to Terehrahda Gillingensis ; 

 but, after further examination, it has appeared to me that the specimen in question may be 

 only a young shell of T. hastata.'] 



Family Spiripeeid^.* 



Of the several genera and sub-genera of which this family is composed, 

 Athp'is, Retzia, Sinnfera, a?id Spiriferina alone have liitherto been found re- 

 presented in the Scottish carboniferous strata. All are provided with spiral 

 appendages for the support of the oral arms. 



Genus Athyris, M'Coy, 1844. (Spirigera, d'Orbigny.) 



The species belonging to this genus bear so much external resemblance to 

 many species of Terebratula, that they were for long referred to that genus ; 

 but they are clearly distinguished by their non-perforated, or fibrous shell-struc- 

 ture, as well as by their internal arrangements. 



The Carboniferous rocks of Scotland have hitherto furnished us with but 

 three species, viz., A. ambigua, A. plam-sulcata, and A. Royssii. 



IV.— Athyris ambigua. Sowerby sp. PL xii., figs. 6-9. 

 S_pinfera ambigua, Sow. Min. Con., vol. iv., p. 105, tab. ccclxxvi., 1822; 

 Atlii/ris ambigua, Dav. Mon. Carb., p. 77, pi. xv., figs. 16-22, and pi. xvii., 

 figs. 11-14. 



In external shape it is more or less obscui'ely pentagonal, and generally 

 rather wider than long. The valves are modemtely convex ; the dorsal one 



* At page 457 and following of the fii'st volimie of " The Geologist" the reader wiU find 

 copious details and illusti-ations in counection with the genera and sub-genera of which this 

 iamilj^ is composed. 



