418 CARBONIFEROUS LAMELLIBRANCHIATA. 



state of preservation does not always allow this character to be observed. King 

 found tlie genus to be present in faunas of Carboniferous and Permian age. 

 Beusliausen Las referred certain Devonian species to the genus ; but, judging 

 from his figures, his shells cannot belong to the genus in question, and he admits 

 that in no single case was a pallial sinus discovered in any of his specimens. In 

 common with Edmondia, Sanguinolites, and TellhiomorpJia, Allorisma possesses a 

 beautifully tuberculated surface. It is also markedly ribbed and sulcated ; but the 

 ribs are simple, and not, as in Edmondia and Sanguinolites, compound or irregular. 

 In addition, the strongly marked oblique ridge of the latter genus is absent, while 

 Edmondia is distinguished at once by the absence of lunule and escutcheon, and 

 by the presence of the ossicle within the umbo. Another anatomical difference 

 between the two genera is the absence of the well-marked ridge behind the 

 anterior adductor muscle-scar, always seen in Sanguinolites. Allorisma has a 

 strong affinity to the other species of the family Coelonotidm {Grariimysiidse 

 of authors), and, notwithstanding the presence of a well-marked pallial line, I 

 think may be justly included within it, just as Yoldia is included in Nuculidae. 



I was for a very long time unable to make out the pallial sinus, but have 

 entirely satisfied myself of its presence in all the species but one, A. Ansticei, 

 which I have included in the genus. M'Coy denied the presence of a pallial sinus 

 in King's shells {op. cit., p. 276), and I was so doubtful of the fact, until the last 

 eighteen months, that in Part I of this Monograph, p. 25, I expressed a doubt of 

 King's observation. I may say, however, that of all workers on the bivalve shells 

 of Carbo-Permian times. Professor King was by far the most accurate and 

 scientific observer, and the majority of genera and species established by him are 

 good. It was King who discovered the hinge in Garhonicola, the ossicle in 

 Edmondia, and the pallial sinus in Allorisma, characters of the utmost importance 

 for the correct understanding of each of these genera. 



As far as I can ascertain at present, Allorisma is (as King has observed, op. 

 cit., p. 197) the oldest form of sinu-pallial shell known, but it possesses no 

 character in common with the Anatinidse, to which family this genus has generally 

 been referred. Tellinomorpha, de Koninck, has, however, a much nearer external 

 appearance to Anatina, but as yet I have not been able to make out that it 

 possesses a sinuated pallial line ; but, reasoning from analogy, I consider it ex- 

 tremely probable that it has this character. Fleming's reference to Hiatella, a 

 synonym of Saxicava, cannot^ of course, be accepted. 



American palaeontologists have recognised the genus Allorisma in Carbonifer- 

 ous rocks of North America. Having been able to study one of the American 

 species, A. siibcuneatus of Meek and Worthen, I have been able to make out that 

 it possesses a sinuated pallial line. This species I can see no reason for separating 

 from A. maxima, Portlock, sp., of which I have considered it a synonym. 



