Report of the State Geologist. 



507 



ifc--« 



From this point the digestive tube extends backward as a simple 

 bent canal, the flexure being toward the pedicle-valve. In 

 inarticulate species it is much longer 

 and more complicated than in Magel- 

 LANIA, Rhyjn< IHONELLA and the articu- 

 lates generally. In Lingula the diges- 

 tive tube is very long and at the oeso- 

 phagus is deflected ventrally ; the 

 stomach is short, rather more circular 

 than elongate and the intestine makes 

 three or four convolutions; in Dis< i.\- 

 isca and Crania there are some varia- 

 tions in the degree of convolution of 

 this tube. In all of the living inarticu- 

 lated species the intestine terminates 

 in a well-defined anus, situated 

 laterally in Lingula, and in 

 the median line in Crania. 



In the articulates the alimentary canal 

 is shorter and much simpler than in Lin- 

 gula, Crania, etc. In Magellania the 

 oesophagus is short, and behind it the 

 tube is slightly contracted, then ex- 

 panding again into a moderately 

 capacious stomach. The intestine is 

 short, and toward its posterior ex- 

 tremity makes a single convolution 

 near the hinge-plate of the brachial 

 valve, and it is probable that, in some 



Of the extinct genera, e. £. ReNSSEL^ERIA, Fig. 12^-Alimentary canal of Lingula 

 o ' C5 ' affinis; a, mouth; b, cesophagus; c, 



Centronella, Athtris, in which this ^ o f 'J^f^*™™*: 

 plate is perforated by a central fora- £»^'^ : T» 

 men, the intestine passed through it. *£*»*• ^ioodTeUisff iS'- 

 The posterior end of the intestine is pha{?eal membrane - (Hancock.) 

 imperforate in all articulated brachiopods, and in Mag ell ania it is a 

 simple point attached to the parietes or lining membrane of the peri- 

 visceral cavity. The presence or absence of this terminal perfora- 

 tion is, therefore, of considerable importance in the classification of 

 these animals, and has been made a basis of subdivision by King, 

 who proposed thereupon the ordinal divisions Tretenterata and 



59 



