372 Zoological Society. 



mia. Like Anomia, it is a thin, hyaline substance, of which the upper 

 valve is a rude convex plate, distorted according to its situation of 

 growth, but slightly notched on one side. Like Peat en, the under 

 valve is characterised by a prominent auricle on the left side, the 

 sinus beneath being very deeply cut in the direction of the hinge- 

 margin, and furnished along the edge with a row of fine erect denti- 

 cles. The hinge, similar to that of Pecten, consists of a slight mar- 

 ginal ligament intersected in the middle by a solid triangular cartilage, 

 situated in the hollow of a superficial depression in each valve. Ap- 

 parently the nearest approximation to this shell may be found in some 

 of the fossil Pectens of the carboniferous limestone, distinguished 

 by a nearer relation with Anomia, of which it presents a reversed 

 condition of growth. 



From the circumstance of one of the valves being perforated by a 

 deep sinus, of which there is no corresponding growth in the other, 

 it may be compared with Pedum, but there is no indication of the 

 umbonal area which characterises the hinge of that genus, and it 

 does not appear to be the production of an animal of the same pecu- 

 liar habits. 



In texture and composition the valves consist of a transparent, 

 semipearlaceous lamina, exhibiting a series of closely- arranged con- 

 centric lines, the interstices between which are minutely rayed with 

 much finer lines. If any importance can be attached to the varia- 

 tions in the microscopic structure of shells for the purposes of classi- 

 fication, the observations with which we have been kindly favoured 

 by Dr. Carpenter on the genus, tend rather to show its affinity w^ith 

 Pedum. There is some uncertainty in the result. " The flat valve," 

 says Dr. Carpenter, " in both specimens is permeated by copious 

 tubuli, a character in which the species agrees with Pedum and with 

 certain species of Lima, and differs from Pecten. This tubularity exists 

 also in the convex valve of the colourless specimen, but is absent in the 

 other (at least in the portion of it which the Bryozoon covering its 

 surface allows me to examine), and I would direct your attention to 

 the fact that the coloured shell possesses a rudimental sculpturing 

 over the whole of its visible external surface, which is totally wanting 

 in the other. Is not this sufficient as a specific difference ? " 



The two specimens here spoken of, collected during the voyage of 

 the Samarang, were dredged by Captain Sir Edward Belcher in the 

 Sooloo Sea, from a coral and stony bottom, at a depth of about four- 

 teen fathoms. The under valve of each is smooth, showing it to 

 have been attached ; the upper valve, covered in part in both speci- 

 mens with particles of coral and parasitic shells, is in one individual 

 smooth and colourless, in the other decussately corrugated, delicately 

 rayed with reddish-orange. The two shells so entirely agree in all 

 other respects that we have not ventured to describe them as distinct 

 species. 



Trusting that this interesting subject may assist the developmental 

 views of Professor Edward Forbes, we have the pleasure of distin- 

 guishing the species by his name. 



