1756 THE VOYAGE OF H.M.S. CHALLENQEE. 



half times as long as the two lateral sides. Nasal odd style of each valve with ten to twelve pairs 

 of branches, about twice as long as the four paired frontal and tergal styles, each of which bears 

 five or six pairs. Terminal coronets three times forked, each with eight straight, spinulate, slightly 

 divergent fingers, shaped like a human finger. 



Dimensiotis. — Length of the shell 3'6, breadth 2'7. 



Habitat. — Central Pacific, Station 272, depth 2600 fathoms. 



3. Coelodecas pentagona, n. sp. 



Shell-mantle about as long as broad ; its frontal perimeter nearly regular pentagonal, with five 

 equal sides. Nasal odd style of each valve with six to eight pairs of branches scarcely longer than 

 the four paired frontal and tergal styles, each of whicli is provided with four to six pairs. 

 Terminal coronets irregularly branched, each with twelve to sixteen slender curved fingers, which 

 bear at the distal end a spinulate knob. 



Dimensions. — Length of the shell 2 '6, breadth 2 '4. 



Habitat. — South Atlantic, Station 332, depth 2200 fathoms. 



Genus 737. Coelostylus,^ n. gen. 



Definition. — C celographida with an odd sagittal frenulum on each galea and an 

 outer lattice-mantle, armed with twelve styles (two odd and four paired styles on each 

 valve). 



The genus Ccelostylus is characterised by the possession of twelve coronal styles ; it is 

 closely allied to Coelos-pathis, and differs from this in the development of a new pair of 

 styles on each valve. These are placed between the odd nasal and the odd sagittal style 

 of each valve, they are directed forwards, and may therefore be called " pectoral styles." 



I. Ccelostylus hisenarius, n, sp. (PL 126, fig. 3a, 3&). 



Shell-mantle one and a third times as long as broad ; its frontal perimeter pentagonal, with a 

 deep median incision at the base ; the two oral sides of the pentagon about as long as the basal 

 odd side, and half as long as the two lateral sides. Sagittal perimeter (fig. 3fl) octagonal ; the 

 three paired lateral sides of the bilateral octagon about equal, and somewhat shorter than the 

 basal and oral odd sides. Equatorial perimeter rounded square. Nasal odd style of each valve 

 with twelve alternate-cruciate pairs of lateral branches, about twice as long as the two paired 

 pectoral styles (each with four pairs), and the odd sagittal style (with six pairs) ; the two paired 

 tergal styles bear eight pairs and are longer than the latter, shorter than the nasal style. All styles 

 are more or less curved, divergent, and at the distal end four times forked, bearing a terminal 

 coronet with sixteen spinulate fingers (fig. 3&). 



Dimensions. — Length of the shell 4-2, breadth 3'2. 



Habitat. — Indian Ocean (Madagascar), Eabbe, surface. 



1 Ccelostylus = Hollow style ; r.ai'hai, aivha;. 



