RECENT BRACHIOPODA 265 



Atremata is a burrowing and prehensile organ, while in all other brachio- 

 pods it is for permanent attachment to a given place. It is true that 

 some discinids do approach the strand, but as they have a more or less 

 centrally placed short and pluglike peduncle and a conical upper valve 

 the waves can have little effect in pulling them from their anchorages. 

 On the other hand, in the articulate brachiopods the peduncle is more or 

 less long and emerges from one valve, so that the animals hang loose at 

 one end of the stalk, a decidedly disadvantageous mechanical defect for 

 holding in tumultuous waters. It is probably for these reasons that most 

 brachiopods avoid the tearing strand-line, and are most abundant in the 

 quiet waters between 50 and 500 feet. 



ARTICULATA GENERA 



l^one of the articulate brachiopods can be relied on to indicate the 

 strand-line, as but 5 approach or live in this zone, and but a single genus 

 appears to be restricted to very shallow water (Megerlina, with its 2 

 species). The other 3 forms prefer deeper water. Of the 129 articulate 

 species about 19 per cent (25 species) live in less than 90 feet of water. 

 Their real habitat, however, is in the deeper water between 90 and 600 

 feet, where nearly 46 per cent (59 species) live. Down to 600 feet occur 

 81 articulate and 28 inarticulate forms, or, in other words, more than 70 

 per cent of brachiopods are at home in these shallower waters. We may, 

 therefore, conclude that the greatest abundance of living brachiopods is 

 in the stormless waters between 90 and about 500 feet of depth. 



None of the 15 rhynchonellids live in very shallow water, nor are any 

 reported in less than 90 feet, but as Hemithyris psittacea is thrown up 

 on the Labrador coast by the storms it is probable that this form lives 

 here not far from the strand-line. The living species are grouped in 4 

 genera, of which Acanthothyris, with 1 form (160 fathoms), Basiliola, 

 with 1 form (200-313), and Cryptopora, with 2 forms (25-2,200), may 

 be regarded as the deep-water genera. Hemithyris has 11 forms, and of 

 these but 2 live between 90 and 288 feet, while the others range down to 

 2,084 fathoms. We therefore see that the rhynchonellids are now deep- 

 water brachiopods, but this certainly was not the case during the Paleo- 

 zoic, where they are frequently found in coarse sandstones, and not at all 

 rarely in mudstones, associated with medium sized and thick shelled lin- 

 gulids. Today they are found in nearly all parts of the oceans, from 

 north of the Arctic Circle to far south in the Antarctic region. While 

 most of the species live in cool waters, at least one (H. cornea) ranges 

 from the warm water off Cape Vincent in 57 fathoms down to the cold 

 waters off Cape Finisterre in 1,093 fathoms. Cryptopora gnomon has 



