104 



THE GEOLOGIST. 



justly observed by Mr. S. P. Woodward, in his excellent Manual on 

 the Mollusca), the dorsal valve must have turned on its long hinge- 

 line with as much precision in the edentulous species as in those of 

 Chonetes and Strophalosia, which were regularly articulated by teeth. 

 It must not, however, be inferred, from the statement here recorded, 

 that the animal ever separated, or required to separate, its valves as 

 widely as could be effected by moving the lid of a snuff-box upon its 

 hinge ; on the contrary, it is probable that the valves were never 

 separated by the animal to the extent of more, at the utmost, than a 

 few lines, as was also the case with the other articulated genera with 

 which we are at present acquainted. 



It has also been stated, and generally believed, that Producta 

 might be distinguished from its sub -genera by the total absence of an 

 area in either valve ; but, although this would appear correct in the 

 generality of species, some exceptional specimens have exhibited a 

 distinct and defined area in the ventral valve.'" In all species of 

 Strophalosia, Chonetes, and Aulosteges, at present known, a triangular 

 or sub-parallel area, of variable dimensions, has been recognized ; and 

 this is larger in the ventral than in the dorsal valve, in which it is 

 moreover divided by a fissure, more or less arched over by a pseudo- 

 deltidium ; the cardinal process of the opposite valve filling up and 

 effectually closing any portion that might otherwise have remained 

 uncovered. 



conclusion. If, therefore, the shells in question belong to Producta, and not to 

 Chonetes (as Professor de Konmck appears disposed to believe), the genus or sub- 

 genus Chonetes would become superfluous, and our notions regarding Producta 

 requhe material alteration, since the genus would be made to contain both eden- 

 tulous as well as strongly articulated species. Such a supposition would demand 

 much fiuther examination and confirmation before being admitted as a definitel,y 

 settled fact. At the time the paper aboA'e referred to was communicated, Mr. J). 

 Shaipe announced that in his opinion fig. 1 alone belonged to Chonetes comoides, 

 and that fig. 2, &c. were referable to another, although closely allied, species. 

 Since that period Professor de Koninck has referred them to Producta Ticmispherica, 

 Sow. There again I nmst be allowed to obser^•e that none of Sowerby's original 

 specimens of the last-named species sliow any area, nor apparently any articulated 

 hinge ; they bear, however, so exact a resemblance to a true Producta that it 

 would l)e necessary to examine a larger lumiber of specimens before I possibly 

 could conscientiously admit the identification to be strictly correct. I am happy, 

 however, to know that my distingniislied friend, Avho has devoted so nnieh time to 

 the study of the species of wliich this family is composed, intends shortly to issue 

 a supplement to his great work, in which he will fully express his views regarding 



* A very remarkable specimen of Producta scmireticuJata, which at one time 

 formed part of Mr. Charles worth's collection, illustrating this feature, has been 

 recently added to the British Museum. This also presents a small pseudo-deltidium. 



