162 J. WILFRID JACKSON ON 



possessing fine, and others coarse, ribbing. In some cases the ribbing is almost 

 entirely obsolete, even in adult examples, a feature already noted by Fischer and 

 Oehlert, and described and figured by them as var. svbmutica (1892, p. 279, pi. xi. 

 figs. 5-6). 



Internally the specimens present many interesting features. In some examples 

 indications of senile conditions are very apparent. The teeth of the ventral valve 

 show considerable enlargement, the muscular impressions are remarkably deep, and the 

 peduncular passage is considerably narrowed by thick deposits of calcareous matter on 

 either side, forming a deep and narrow channel. The foramen is reduced to a very 

 small size (PL II. fig. 11). 



In no case, however, are the deltidial plates absorbed, as is often the case during 

 senile decay. 



In the dorsal valve similar conditions are to be seen. Here the cardinal process is 

 of notable size and the brachial support of extreme tenuity. (See Fischer and Oehlert, 

 1892, pL ix. fig. 6). 



Similar evidences of senility are present externally in the thickening of the lateral 

 and frontal margins and the crowding together of the growth lines (PI. II. fig. 12). 

 (See also Fischer and Oehlert, 1892, pl. ix. figs. 3-4.) 



The various young examples of this species, obtained mostly from the tests of 

 Cephalodiscus, range in size from 1 to 6 mm. and show an interesting series of growth- 

 stages in the brachial support. This feature has already been very ably described by 

 Fischer and Oehlert (1892), and as the above specimens exhibit no important points 

 of difference, it will not be necessary to deal with them again here. 



Tei-ebratella dorsata appears to be restricted to the immediate neighbourhood of 

 South America. It is an abundant species in the Magellan Straits, the littoral of Tierra 

 del Fuego, and Falkland Islands. On the east coast of Patagonia it does not appear 

 to range further north than latitude 52° S. (near Cape Virgins) and the Falkland 

 Islands. On the West Patagonian coast it seems to possess a more considerable 

 extension, having been recorded from Valparaiso and Coquimbo, Chili. 



A more distant locality has been recorded for this species by Davidson (" CJiall." 

 Report, p. 44), viz. Royal Sound, Kerguelen, but Blochmann (1906), from a study of 

 the original examples, has shown this record to be erroneous, the specimens in question 

 being an entirely new species, Terebratella enzenspergeri, Blochmann. 



The bathymetric range of T. dorsata, according to recent authorities, is from about 

 5 to 120 fathoms. 



In the report on the fossil Brachiopoda of the Swedish S.-P. Expedition, Buckman 

 (1910) has described a new species of Magasella (M. antarctica) which appears to 

 me to present certain definite resemblances to Terebratella dorsata (Gmelin). 



The fossil species, which comes from the Glauconitic Bank formation (Pleistocene) 

 at Cockburu Island, off Graham Land, West Antarctic, is described and figured by 

 Buckman (1910, p. 18, pl. i. figs. 17-I7d), with the remark that Terebratella 



(ROY. SOC. EDIN. TRANS., VOL. XLVIII., 384.) 



