60 



PALAEONTOLOGY. 



ings of the body on which it grows, like the oyster and 

 Anomice. The pallial impressions are like those of Orthis, 

 and the form of the spiral arms is indicated by prominences 

 wdiich almost fill up the interior of the shell in aged examples. 

 Some indications have been obtained of slender calcareous 

 spires for the support of the arms in this genus ; and also in 

 Koninckia, a small shell from the trias of St. Cassian, in which 

 there are always spiral grooves in the interior of the valves 

 crossed by the impressions of the pallial sinuses. 



The anomalous fossil called Calceola sandalina (Lam., fig. 

 13, 6) is also peculiar to the Devonian limestones. In shape 

 it resembles Cyrtia, but has no hinge, and neither foramen nor 

 internal processes, except a row of small projections along the 

 hinge-line, and two small lateral groups of ridges in the 

 smaller valve. The interior is punctato-striate, but has no 

 recognisable muscular markings. 



The Produdidw are altogether palaeozoic fossils, and most 

 abundant in the carboniferous limestones. Their valves are 

 concavo-convex, the hinge-line is straight, and the interior 

 is marked with simple vascular spaces, and with distinct im- 

 pressions of the muscles for opening and closing the valves. 

 There are 60 species of Producta found in the upper palaeozoic 

 rocks, having a very wide range in North and South America, 

 and dispersed from Spitsbergen to Thibet and Tasmania. Some 

 of them are extremely variable in form ; many are armed with 

 long tubular spines, and others completely clothed with short, 

 hair-like processes ; they have no hinge-teeth, and the hinge- 

 area is extremely narrow, except in the sub-genus Aulosteges of 

 the Eussian zechstein. Producta proboscidea has its convex- 

 valve prolonged into a tube, as if for the constant supply of 

 respiratory currents. The Permian genus Strophalosia has its 

 valves articulated by hinge-teeth, and covered with long and 

 slender hollow spines ; the shell is attached when young by 

 the umbo of the large valve. CJionetes (fig. 13, 5) is distin- 



