133 INTRODUCTION. 



Animal unknown. Shell oblong oval, inequivalve ; valves unarticulated ; larger or 

 ventral valve most convex, with a straight, thick, perforated, conical beak, more or less 

 removed from the hinge line ; foramen circular or elongated, opening on the back of the 

 beak, and communicating with the interior of the shell by a cylindrical tube or siphon, 

 destined to afford passage to the muscle of attachment ; no area nor deltidium ; each valve 

 has a wide, crescent-shaped cardinal edge, covered by numerous horizontal lines of growth. 

 Smaller valve slightly convex and depressed, the hinge-line forming an arch which merges 

 imperceptibly into the lateral margins. Structure calcareo-corneous, vi^ith a distinctly 

 punctured structm'e arranged in tubular layers ; surface smooth, but presenting lumierous 

 lines of growth, and scattered or closely packed, slender, hollow spines, dilated at their 

 base, and somewhat quincuncially arranged ; no calcified supports for the arms. Muscular 

 impressions unknown. 



Obs. One of the species composing this remarkable genus was noticed in 1829,^ but 

 it was only in 1845," that M. de Verneuil established the genus Siphonotreta, Avhich has 

 been recognised and adopted by all subsequent naturalists, on account of the clearly 

 defined characters which separate it both from Crania and Terebratula, where it had been 

 located, as well as from all the other genera. 



Subsequent and most valuable information was thrown on the subject by the memoir 

 of Dr. Kutorga,^ in which beautiful illustrations and structural details had been delineated 

 with the greatest care. Mr. Morris, who first determined its occurrence in England, (from 

 a specimen in the cabinet of John Gray, Esq., of Dudley,) has likewise added some details.* 

 M. de Verneuil pointed out that Siphonotreta should be placed near Lingula and Blscina, 

 but it is distinguished from the first by the pedicle not passing between the beaks, and 

 from the second by the form of the perforated valve. I differ, however, from my learned 

 friend in his belief that the perforated beak of Siphonotreta corresponds to the imperforate 

 one of Terebratula. Mr. Morris considers the genus allied to Cra^iia; and Professor King 

 places it in his family Craniada. Professor Forbes includes Orbicula and Crania in the 

 same family. My views coincide with those of M. de Verneuil, and I prefer placing it with 

 Dismiidce, because the shell differs materially from Crania by its remarkable siphon or 

 pedicle opening, no such aperture being visible in any species of the last named genus, 

 while it would be nearly related to Discina and Orbiculoidea by being fixed by a pedicle 

 issuing from an aperture. Its spines cannot be made use of as a generic character of much 

 value, the same being common to other genei-a. Mr. Morris states that the spines ai-e 

 moniliform in the English species, a character not yet found in the Russian types. 



1 Professor Eichwald ; Zoologia Specialis (C. unguiculala). 



2 Russia and Ural Mountains, vol. ii, 184.5. 



^ Uber die Siphonotretaeae, by Dr. S. Kutorga, Verhandlungen der Kaiserlichen Miiieralogischeu 

 Gesellschaft fur das Jalir 1847. 



* Annals and Mag. of Nat. Hist., vol. iv, 2d ser., 1849. 



