GENUS DICHELASPIS. 115 



Caudal Appendages about half the length of the lower 

 segments of the pedicels of the sixth cirrus ; truncated and 

 rounded at their ends; thickly clothed with long excessively 

 fine bristles, so as to resemble camel-hair pencils. 



The Stomach, I believe, is destitute of caeca ; in it was 

 a small crustacean. 



General Remarks. — I was at first unwilling to sacrifice 

 Mr. Hind's genus, Trilasmis, which is so neatly cha- 

 racterised by its three valves ; moreover, the present 

 species does differ, in some slight respects, from the 

 other species of Psecilasma; but under the head of 

 P. jissa I have shown how that species, P. crassa and 

 P. eburnea are tied together. The absence of terga, 

 which are rudimentary in P. crassa, (and we shall here- 

 after see, in Conchoderma, how worthless a character their 

 entire absence is,) and the arrangement of the spines 

 in the upper segments of the posterior cirri, are the only 

 characters which could be used for a generic separation. 



Genus — Dichelaspis. Plate II. 



Octolasmis. * /. E. Gray. Annals of Philosophy, vol. x, new series, 



p. 100, August 1825. 

 Heptalasmis. Agassiz. Nomenclator Zoologicus. 



Vahce 5, qua fere pro septem haberi possent, scuto in 

 segmenta plane duo, adangidum auteni rostralem conjuncta, 

 diviso : carina pier unique sursiini inter terga externa, 

 deorsum aid disco infosso autfurcd aut calyce terminata. 



* From hxrfkoa, bifid, and acnria, a shield, or scutum. The name Octo- 

 lasmis was given by Mr. Gray under the belief that there were eight valves. 

 Leach (as stated in the 'Annals of Philosophy/) had proposed, in MS., 

 the name Heptalasmis, and this is now used in the British Museum by Mr. 

 Gray, and thus appears in Agassiz's ; Nomenclator Zoologicus.' Although, 

 strictly, there are only five valves, 1 continued to use, in my MS., the term 

 Heptalasmis, until I examined the D. orthogonia, where it was so apparent 

 to the naked eye that there were only five valves, the scuta in this species 

 being less deeply bifid, that I was compelled to give up a name so mani- 

 festly conveying a wrong impression, and hence adopted the one here used. 



