264 CONFERENCE ON PALEOZOIC PALEOGEOGRAPHY 



attain an average age of 5 years or even more. Yatsn kept them alive in 

 aquaria with the water fetid, and Morse did the same, keeping his speci- 

 mens alive for six months in almost unchanged water. Joubin kept 

 Crania, taken from great depths, alive in jars under very adverse condi- 

 tions for 14 months. In these statements we see the very adverse condi- 

 tions under which the burrowing Lingula may live, and that the tenacity 

 of endurance is also very great with cemented Crania. In this adapta- 

 bility lies the probable explanation of why the lingulids and craniids have 

 lived since the Ordovicic. Lingula and Crania have endured all of this 

 vast time apparently without change other than the superficial ones of 

 form, size, and ornamentation. * 



We may therefore conclude that inarticulate brachiopods when large, 

 thick shelled, and abundant clearly indicate to the paleontologist animals 

 inhabiting very shallow waters of probably less depth than 100 feet. 

 Further, that these waters were in close proximity to the shores and 

 probably were warm. Crania is the only genus inhabiting shallow waters 

 of the cooler areas and essentially those of the northern hemisphere. The 

 immediate shoreline, and often the estuarine bays and deltas, will be 

 indicated especially by the large lingulids embedded in muds arid sands 

 with an otherwise sparse fauna. When the species are small, but not 

 minute, still somewhat thick shelled and the individuals abundant, it is 

 probable that the sediments of such waters were also those of the shal- 

 lows — that is, ranging between 50 and 200 feet, with the possibility of 

 even 400 feet. Minute inarticulates are not safe guides to bathymetric 

 depth in Paleozoic time, and their habitat significance must be judged 

 more from the associated fossils and the character of the entombing sedi- 

 ments. The Atremata, after the Cambric, appear always to have pre- 

 ferred shallower waters near the strand-line, while the Neotremata, 

 though also lovers of shallow waters, appear to have preferred to keep 

 away from the immediate strand. These slightly varying habitats have 

 their probable explanation in that all the Atremata, after the Cambric 

 (lingulids), lived in burrows, while those of earlier times (obolids) ap- 

 pear to have lived above the bottom, fastened to foreign objects by a more 

 or less long peduncle. On the other hand, the Neotremata are never 

 burrowers, but are fastened to some object above the ground by a very 

 short peduncle that issues directly through some part of the ventral 

 valve, as in the highly modified bivalve Anomia. We see, therefore, that 

 the burrowing lingulids are protected from wave action, and that their 

 holes are always full of water, while the discinids live above the bottom, 

 and because of their very much cramped shell space would, at low tide, 

 be without water for hours. Further, the peduncle in Lingula and the 



