ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 969 



Relations of the Successive Brachiopod Faunas. 



I. The Ballantrae rocks have so far afforded such poorly preserved material and 

 so scanty a number of brachiopods that it is impossible in the present state of our 

 knowledge to give a satisfactory survey of their characteristics. We may note, 

 however, that all the. forms belong to the Atremata, and with the possible exception 

 of one species none occur in higher beds. 



II. The Stinchar Limestone Group has yielded, on the other hand, a plentiful 

 variety of species and individuals. Sixty species and varieties are now recorded. 

 Most of these are peculiar to this horizon or to the Girvan area, but about 20 of the 

 total number range up into the overlying group. 



III. The richness of the Balclatchie Group in brachiopods is remarkable, about 70 

 species or varieties being recognised. The majority are limited to this group of 

 beds, and none of the peculiar local forms pass up into the Whitehouse Group. 



IV. Only 34 different forms occur in the Whitehouse Group, and of these about 

 20 are positively limited to it. A few of the others are found in the overlying 

 Drummuck Group, but practically none range down into the underlying beds. 



V. The Drummuck Group contains over 40 species and varieties at present 

 recognised, and a few forms such as Dayia cymbula, var. girvanensis, Christiania 

 tenuicincta, and Triplecia insularis have come up from the Whitehouse Group. 



VI. The Mulloch Hill Group ushers in the Silurian fauna, and its connection with 

 the older faunas is slight. Even such long-ranging forms as Lept. rhomboidalis are 

 represented by distinct varieties. But new genera, especially pentameroids, rhyn- 

 chonelloids, and spire-bearing species make their first appearance. Twenty-nine 

 species and varieties of brachiopods from this horizon have here been described. 



VII. The Saugh Hill Group has furnished 42 different species and varieties, 

 several of which have occurred in the underlying group. But new forms preponder- 

 ate, and these ally it more closely with the succeeding Camregan Group. 



VIII. In the Camregan Group 27 different brachiopods have here been recorded, 

 but most of these come from the locality termed Bargany Pond Burn and are 

 Penkill species, so that the individuality of the brachiopod fauna of this group is 

 not marked, and the occurrence of some of the species rests on doubtful evidence. 



IX. The Penkill Group has yielded 25 species or varieties. Several of these 

 range up from the Saugh Hill Group, or occur in the Camregan Group. Parastrophia 

 rotunda, Philhedra penkillensis, Strophoyiella penkillensis, and perhaps Orthis poly- 

 gramma, var. pentlandica, seem to characterise it and to be restricted to it. 



Affinities of the Fauna. 



In the Stinchar Limestone and Balclatchie Groups we have been led to note the 

 close relations of many of the species with American rather than with English or 

 North European forms. * In the Whitehouse and Drummuck Groups these affinities 



* This feature is also observable in other zoological groups, e.g. the Bellerpphontacea. 



