CLASSIFICATION OF THE BRACHIOPODA. 



69 



again by two additional processes, departing from the reflected portion of the loop to 

 the central septum. The cirrated arms are large, their fringes extending to near the 

 border of the shell. On either side of the mesial septum are seen the double scars 

 produced by the adductors. 



Obs. Prof. King proposed to distinguish those species possessing a triply attached loop 

 from Terebratula and Terebratella, by the name of Megerlia ; but after a minute exami- 

 nation of the three or four species at present known, and which seem to vary from one 

 another to some extent in the details of their loop, it will be preferable for the present to 

 admit Megerlia simply as a section of Terebratella. The M. truncata has been by some 

 authors placed in the genus Orthis, but it in no way possesses the characters of Dalman's 

 genus. The interior of the valves, especially in the last-named species, are covered with 

 spinulose asperities which radiate from the base of the hinge Une to the margin, a character 

 likewise observable in some species of Prodicctiis. 



Geol. range. — In the present state of our knowledge the first species appeared during 

 the cretaceous period, and continued under different forms up to the present day. 



Examples : M. truncata, Gmel. ; M. lima, Def. ; pulchella, Sow., sp. 



Genus Kraussia, Davidson, 1852.^ 



Type—K. KUBRA, Pallas, sp.2 Int., PI. VI, figs. 28, 29. 



Anomia, Chemnitz, Gmelin, &c. 

 • Tekebratula (part), of the generality of Authors. 



Shell subcircular, with a nearly straight hinge line ; beak truncated ; foramen large, 

 round ; deltidial plates small, not united ; beak ridges well defined, leaving a flat false area 

 between them and the hinge margin ; in most species a longitudinal depression exists in 

 the smaller valve : external surface smooth or variously plaited, structure punctated : the 

 dorsal pedicle muscles produce two wide eye-shaped impressions close to the hinge, and be- 

 tween the inner walls of the socket ridges, a small slightly elevated mesial ridge extends to 

 about haK the length of the valve, at the extremity of which arise two small forked diverging 

 lamellse expanded at their extremity. The cirrated 

 arms are unusually small, their fringes not extend- 

 ing to more than half-way towards the border of 

 the shell ; in the first part of their course from the 

 mouth forward, the cirri are few or wanting : the 

 whole brachial apparatus is supported by the small 

 forked process above described, no other part of 

 the apophysary system being calcified : cardinal process or boss, small. 



Fig. 13. 



Fig, 14. 



13. Kraussia rubra {dorsal valve). 



14. Kraussia Lamarckiana (animal). 



' Annals and Mag. of Nat. Hist., vol. ix, 2(1 series, p. 369. 

 2 Mis. Zool., tab. xiv, figs. 2, II. 17C6. 



