384 Mr. J. E. Gray on the Arrangement of 



4. M. obtecta. Ph. o., Sow. Thes. f. 80, 81. 



5. M. carta. Ph. curta, Sow. Thes. f. 33, 34 & 105. 



*** Valves with a single subcentral impressed rib ; the anterior 

 dorsal reflection erect, separate from the outer surface of the 

 valve. 



6. M. striata, Leach. Ph. striata, Linn., Sow. Thes. f. 40-44. 



Ph. lignorum, Spengler. Ph. nana, Pultney. Ph. pusilla, 

 Linn. P. conoides, Flem. Ph. clavata, Lamk. 



Jun. ? Ph. falcata, Wood. 



Var. produced behind. Ph. semicostata, Lea, Sow. Thes. f. 84, 

 85. Junior, Ph. terediniformis, Sow. Thes. f. 97, 98. 



7. M. australis, Gray. Shell elongate, front portion with rather 



distant waved concentric ridges (fewer than in M. striata), 

 the hinder portion smooth, slightly concentrically waved ; 

 periostraca very thin, simple. 

 Hab. N.W. Australia, in hard stone and in resin. 



8. M. rivicola. Ph. r., Sow. Thes. f. 90, 91. 



9. M. aperta. Junior, Ph. aperta, Sow. Thes. f. 99, 100. 



10. M. cuneiformis. Ph. cuneiformis, Say, Sow. Thes. f. 38, 39, 

 f. 86, 87. Ph. corticaria, Adams, Sow. Thes. f. 94, 95. Ph. 

 Edwardsii and Ph. rudis, Gray, B. M. 1820; junior, Sow. 

 Thes. f. 96. 



7*. Teredina, Lamk. Fistulana, sp. Lamk. Teredo, J. Sow. 



This fossil genus appears only to differ from Martesia in being- 

 provided with a conical continuous entire tubular prolongation 

 at the hinder end of the valves, in the place of the elongation of 

 the valves, which is often to be observed in that genus, and in 

 the absence of any supplementary posterior or ventral valves. 



1. T. personata, Lamk. Teredo antenautse, /. Sow. 



c. Siphons with shelly or rarely horny valves surrounding their base 

 and forming a cup-like appendage on the hinder extremity of 

 the valves. 



These appendages are not to be confounded with the exten- 

 sions of the periostraca which are to be observed on the surface 

 of the hinder part of some Martesice, as M . obtecta and M . con- 

 camerata. 



8. Pholadid2ea, Turton, 1819. " Pholadidoidea, Goodall,' 3 

 Blainv. Pholidse, Swainson. Parapholas, part., Conrad. 



* Siphonal valves without any tubular elongation, and not folded. 



1. Ph. papyracea. Ph. p., Sow. Thes. f. 66. Junior, Ph. lamellata, 



Turton. P. striata, Blainv. t.80. f. 7. 



2. Ph. spathulata. Ph. s., Sow. Thes. f. 69, 70. 



