54 



19. ducalis, Chemn. 



20. electrum, Reeve. 



21. erinaceus, id. 



22. flabelluin, id. 



23. foliaceus, Chemn. 

 21. fragilis, Sow. 



25. fragum, Reeve. 



26. gilvus, irf. 



27. Gussoni, Cosfa. 



28. gsedaropus, Linn. 



29. histrix, Reeve. 



30. ictevicus, zrf. 



31. imbutus, z'rf. 



32. imperialis, Chemn. 



33. Lamarckii, id. 



34. Layardi, Reeve. 



35. leucacantha, ifrorf. 



36. limbatus, -So?o. 



37. lingua-felis, zrf. 



38. lougitudinalis, Lam. 



39. microlepos, irf. 



40. multimuricatus, R. 



41. multisetosus, z'rf. 



42. mus, Chemn. 



43. Nicobaricus, id. 



44. uudus, «/. 



45. nux, Reeve. 



46. ocellatus, erf. 



47. Pacificus, id. 



48. pictorum, Chemn. 



49. plurispinosus, jR. 



50. princeps, Brod. 



51. radula, Reeve. 



52. ramosus, irf. 



53. regius, Linn. 



54. rubicundus, .#. 



55. setiger, id. 



56. Sinensis, £o?#. 



57. spectrum, Reeve. 



58. tenebrosus, id. 



59. tenellus, z'rf. 



60. tenuispiuosus, Sow. 



61. unicolor, z'rf. 



62. ustulatus, Reeve. 



63. varians, £o?p. 



64. variegatus, Chemn. 



65. vexillum, Reeve. 



66. violaceus, z'rf. 



67. virgineus, z'rf. 



68. zonalis, Chemn. 



Figure. 



Spondylus croceus. PI. 27. Fig. 160. Shell, illustrative of the vivid 

 colouring and branching sculpture of the genus, but showing only a 

 small development of the umbonal area. 



Genus 2. PLICATULA. 



Animal ; supposed to be similar to that of Spondylus. 



Shell ; affixed, irregular, inequivalve, attenuated toivards the hinge, 

 not auriculated ; margins mostly plicated ; umboes unequal ; no 

 umbonal area ; hinge composed of two strong teeth in each valve 

 closely interlocking. 



The genus Plicatula comprises only a few recent species, but it holds 

 an important place in fossil conchology, and the species are distinguished 

 by a marked uniformity of character. Like Spondylus, the hinge consists 

 of two pairs of closely-interlocking teeth ; no umbonal area is, however, 

 formed as in that genus, and the shells are uniformly small, characterized 

 by a speciality both of sculpture and colour. There is no indication of 

 fronds or prolonged spines, and the shell is always of a dull reddish-brown, 

 unrelieved by any variety of painting. 



The species are from Western America, Australia, and the Philippine 

 Islands. 



