48 On the Bilobite. 



lower part of fig. 3. must be considered as corresponding to 

 the posterior slope or areola of the cardium, the upper portion 

 as corresponding to the anterior slope or area, and the dorsal 

 furrow, figs. 1.2. 3. to the base. The transverse costse may 

 be supposed to correspond with the longitudinal furrows on the 

 surface of the cardium, and continued to what has been 

 described as the anterior part of the inferior surface of the 

 Bilobite. The raised zigzag line may be considered as 

 formed by the terminations of the costae of the shell not being 

 exactly applied to each other, and thus leaving an intermediate 

 substance between them. Perhaps a clearer idea may be con- 

 veyed, by supposing a cardium to be compressed in the direc- 

 tion of a line drawn from the beaks to the base, so as to bring 

 these parts nearly into contact. A question then arises, whe- 

 ther this apparent compression is accidental, or characteristic, 

 of a species ? It has been urged, that shells, from their usually 

 delicate and brittle texture, cannot be distorted without in- 

 jury ; but it is well known, that Echini, &c. which are 

 equally delicate, are often found in this state. That this com- 

 pression is not accidental, is, it is supposed, evident from the 

 fact, that all these Bilobites have the appearance of being com- 

 pressed in a similar direction, a character which is too con- 

 stant to have been occasioned by accidental causes. From these 

 observations, it is evidently a futile attempt, in the present state 

 of our knowledge respecting these fossils, to distinguish them 

 into separate species. The term Bilobite may be retained as 

 a distinctive appellation, comprehending casts of several ex- 

 tinct species of cardium, from the above mentioned localities. 



The specimen figured 3. 4. was submitted to the inspection 

 of our distinguished zoologist, Mr. Say, who has politely fa- 

 voured us with his opinion : " I have no doubt that it is a bi- 

 valve shell, of the genus Productus of Sowerby. It has lost 

 its original form, in consequence of great pressure of the su- 

 perincumbent strata, applied in the direction of the height of 

 the shell. That the original form of organic remains is often 



