MOLLUSCA. 73 



The observations to be derived from the microscopic structure of Hemipecten, which has 

 been kindly exhibited to us by Dr. Carpenter, are, however, singularly contradictory to the 

 views presented by its external characters. Of the two specimens collected, the texture and 

 composition of both valves consist of a hyaline semi-pearlaceous lamina, presenting a series of 

 closely-packed concentric lines, the interstices of which are minutely rayed with much finer 

 lines. Submitted to the microscope, the flat valve in both specimens (Fig. la, 2d) is 

 permeated by copious tubuli, a character in which the genus agrees with Pedum and with 

 some species of Lima, and differs from Pecten. This tubularity Dr. Carpenter observed to 

 exist also in the upper valve of the colourless specimen (Fig.l c), but not in the other (Fig. 2 c), 

 so far as the Bryozoon upon its surface allows of an examination. 



The upper valve of the coloured specimen (Fig. 2 c) possesses a rudimental sculpturing 

 over its entire surface ; but as it may have received this from the parasite, and exhibits no 

 other appreciable poiut of difference, we have not ventured to distinguish it specifically from 

 the white specimen. 



1. Hemipecten Forbesianus. PI. XX. Hemip. testa orbiculari, Anomiaefbrmi, tenuissima, hya- 

 lina, concentrice lineata, linearum interstitiis eximie reticulatis, valva iuferiore plauulata, auricula lon- 

 gitudinaliter radiata, sinu profuudo, valva superiore convexa, vix auriculata; pellucido-alba, valva superiore 

 interdum rufo-aurantio radiata. 



Hab. Sooloo Archipelago, Eastern Seas (dredged from a coral and stony bottom at a depth of about 

 fourteen fathoms) ; Belcher. 



Two specimens of this interesting new form were collected during the voyage, one 

 smooth and white, the other slightly sculptured in a decussately corrugated style, probably 

 from the effect of the Bryozoon which covers it, and rayed with orange-red. The under 

 valve is smooth in both specimens, showing it to have been attached ; the upper valve is 

 more or less covered in both with various parasitic objects. 



We have the pleasure to name the species in honour of Professor Edward Forbes, who 

 notices the genus, in his valuable work on the British Mollusca, as affording a curious inter- 

 mediate link between Pecten and Anomia. 



Plate XX. Fig. 1 represents the smooth colourless specimen ; a, interior of the under valve ; b, the valves 

 closed, presenting the exterior of the under valve ; c, the valves closed, presenting the exterior of the upper valve. 

 Fig. 2 represents the coloured and slightly corrugated specimen ; a, interior of the upper valve, which is not 

 shown of the former specimen ; b, the valves closed, presenting the exterior of the under valve ; c, the valves closed, 

 presenting the exterior of the upper valve; d, interior of the under valve : — all of the natural size. 



73. PECTEN, Bruf/uiere. 



1. Pecten Reevei. PI. XXI. Pig. 10 a, b. Pect. testa sequivalvi, subaequilatera, suborbiculari, 

 paululum longiore quam alta, alba, carmineo vivide variegata et radiata et violaceo maculata ; costata, costis 



u 



