CLASSIFICATION OF THE BRACHIOPODA. 53 



readers of the fact that certain families are entirely composed of punctated, others of icn- 

 punctated species, while a few are made up of genera, which seem to assume both con- 

 ditions. Spinose and foUaceous expansions cannot be considered of generic importance, 

 since they occur in some species of most genera. 



Coloration cannot be made use of as a generic character, and its value to the Palaeonto- 

 logist is small ; but when occurring on fossil forms it should always be noted. Prof. Forbes 

 has kindly informed me, " that his observations on the distribution in depth of recent 

 species have led him to the conclusion that definite patterns, i. e., stripes, bands, and 

 waves of colour vividly marked, do not occur, except in rare instances, on shells living 

 beyond moderate depths, as below fifty fathoms or thereabouts, and that thus we may be 

 enabled to come to approximate conclusions respecting depths of ancient seas from the 

 patterns preserved to us on fossil shells." The coloration is of some use in distinguishing 

 the recent forms of Brachiopoda, green, yellow, red, and blueish-black being the prevailing 

 colours; several forms are striped or spotted with red. Among the fossil species some 

 examples have preserved traces of their colours, as already mentioned in Part III, p. 6, and 

 several other examples will be hereafter noticed, so that in all probability the species now 

 extinct, when alive, presented all the rich varieties of tint observable in the present 

 inhabitants of our seas. 



Muscular Impressions. — We will now briefly notice those impressions left by the 

 muscles in the interior of the shell in the different genera. The character of several of 

 these in Lingula, Discina, Crania, Terebratula, and Hhynchonella, had been pointed out 

 in 1802 and 1833 by Cuvier and Prof. Owen, but since that period considerable progress 

 has been made, and we are already sufficiently acquainted with the bearing of the majority 

 of these in the forms now alive to venture to interpret their homologues in the fossil, 

 extinct genera ; but further researches on the function of certain of these, especially in 

 Lingula, Discina, and Crania will be necessary before the subject can be considered 

 completely and finally settled. 



Professor Owen has made known his most recent views on the muscular system of 

 Terebratula in the first chapter of this Introduction.^ 



Three kinds of muscular impressions particularly interest the Palaeontologist. 



I. The Adductor {valvular muscles of King, Adductor longus, anticus, awd posticus, ot 

 Professor Owen) leaves in the dorsal or socket valve of all the articulated genera four 



^ The account which I have given of the muscular system of the recent Brachiopoda is also derived 

 from a personal examination of the animals of all the recent genera, aided by the important Memoir of 

 Professor Owen, in the 'Zool. Trans.' for 1833, and that of Professor King, in his work on the ' English 

 Permian Fossils,' published by the Palaeontographical Society in 1849. These examinations, and their 

 application to the muscular impressions in the extinct genera, were made in conjunction with Mr. Woodward, 

 (as stated in the ' An. Nat. Hist.' for May, 1852). 



Since then, Professor Owen kindly offered to publish, in my Introduction, the valuable materials 

 accumulated in his researches during the last twenty years ; but after comparing the learned professor's 

 printed proof with my own, I find that he has given to some of the muscles names differing from those 



