124 INTRODUCTION. 



shortly after (1768,) Linnaeus changed the term to Anomites craniolaris. The genus 

 was founded by Retzius,^ m 1781, on the first of Stoboeus's types ; Poh, in 1791, figured 

 the animal of a recent species, which he termed Criopus ;~ but Miiller had before him, in 

 177G and 1781, described another recent form, picked up on the coast of Denmark, under 

 the name of Patella anomala!" This shell has proved the subject of lamentable confusion ; 

 Cuvier, believing it distinct from the Crania of Retzius, proposed for it the generic 

 appellation Orhicida^ a name which must unavoidably be expunged from the nomenclature 

 and placed among the synonymes of Crania, since the so-called Patella anomala un- 

 doubtedly belongs to the last-mentioned genus.^ Professors King" and M'Coy^ have 

 proposed to split the genus Crania into several sections, but I do not consider the 

 points brought forward of sufficient value. The first of these authors limits the genus 

 Crania to species similar to C. Ignabergends^ which are only attached by a small 

 portion of their lower valve, and proposes the term Criopus for those (C. turbinatus, 

 Parisiensis, 8fc.) affixed by the entire surface of the same valve ; but this character falls to 

 the ground, from the fact that the same species sometimes assumes both modes of 

 attaclynent,^ and some were probably entirely free; nor do the internal dispositions of 

 the muscular impressions warrant us to suppose that the animal was different in 

 either case. Professor M'Coy proposes two other genera. Pseudo-crania and Spondylohus. 

 The first is established on two Silurian species, the C. antiquissima, Eichw., sp., and 

 P. divaricata, M'Coy, both are stated to have been unattached, but, as above observed, 

 some well-known Cretaceous Cranias presented the same characters ; the muscular 

 scars in Professor M'Coy's species are very similar to those of Crania, the chief dis- 

 similarities pointed out would appear to consist in the margin of the shell being smooth, 

 or wanting the produced granulations, and in the vascular impressions ; but these cha- 

 racters vary likewise to a great extent in different species of Crania. The Professor's 



^ Crania oder, &c., Berlin Gesellsch. Schrift, Brand ii, p. &(i, 1781. 

 2 Testacea utriusque Sicilise, vol. ii, p. xxv, fig. 24. 



* Zoologia Danica, 1777, tab. v, fig. 1 — 7. 



* Cuvier; Tableau Elementaire du Regne Animal, p. 435, 1798 — " Les orbicules {Orbicula) 



On ne connait de ce genre qu'une seule espfece {Patella anomala) — Miiller." Refer likewise to Cuvier's 

 celebrated "Memoir sur I'Animal de la Lingule," 'Mem. du Mus.,' vol. i, 1802, in which he again states 

 that P. anomala is the type of his genus Orbicula. — Lamarck's views were exactly the same as those 

 of Cuvier, as may be seen by referring to the ' Systeme des Anim. sans Vert.,' p. 140, 1801. — Bruguiere 

 does not appear to have been the first proposer of the genus Crania, as stated by Dr. J. E. Gray, in the 

 'An. of Phil.' for 1825. 



' The species described by myself under the name of Orbicula, in Part I, p. 7, and III, p. 9 and 10, do 

 not belong to the genus Crania, but to Discina of Lamarck. 



8 A Monograph of English Permian Fossils, p. 84, 1849. 



7 British Pal. Foss. in the Camb. Mus., pp. 187 and 255, 1852. 



* The first-mentioned species by Retzius is the C. Brattenburgensis = nummulus of Lamarck. 



9 See Part II, p. U. 



