MONOGRAPH OF THE EXISTING CRINOIDS. 623 



TUNICATA. 



Small tunicates, both simple and compound, are occasionally found on the 

 stems and cirri of the pentacrinites ; large ones are extremely rare. 



ENTEROPNEUSTA. 

 RHABDOPLEURA MTRABILIS (BARS). 



This form was found by Sars growing along the column of Rhizocrinus lofo- 

 tensis; it was originally recorded as a polyzoan under the name of Halilophus 

 mirabUis. 



CRUSTACEA. 



DBCAPODA MACRUHA. 



Family ALPHEID^. 



The family Alpheidse includes a considerable number of partially and strictly 

 commensal types, among which may be mentioned Arete maruteensis Coutiere, 

 which lives among the spines on the oral surface of the large sea urchin Hetero- 

 centrotus mamillatus Klein, Arete dorsalis var. indicus Coutiere, which Professor 

 Coutiere found at Jibuti, French Somaliland, living among the spines on the oral 

 surface of another sea urchin of the same family, Echinometra mathcei (de Blain- 

 ville), the alpheids in both cases resembling the hosts in color, and a number of 

 the species of the genus Synalpheus commensal on gorgonians, Solenocaulon, and 

 comatulids. When these animals are more extensively studied in the field undoubt- 

 edly commensalism will prove to be much more frequent than is now supposed. 



All of the alpheids commensal on comatulids belong to the genus Synalpheus. 

 This genus as now understood includes 63 species and 15 varieties; of these 78 

 recognized forms only 4 occur on crinoids, 2 of these invariably, so far as known, 

 the other 2 being varieties of species the commensalism of which has not been 

 established. 



The genus Synalpheus falls into six well-characterized groups, of which one, 

 the so-called " Comatularum Group. 1 ' includes all the forms commensal on crinoids. 



The species in the Comatularum Group are the following, those known to be 

 commensal on comatulids being designated by an asterisk (*) : 



* Synalpheus comatularum (Haswell) [=$. falcatus Sp. Bate]. 

 Synalpheus stimpsonii stimpsonii de Man. 



*Synalpheus stimpsonii maldivensis Coutiere. 

 Synalpheus carinatus carinatus (de Man). 

 *Synalpheus carinatus l)inongcensis de Man. 

 Synalpheus carinatus ubianensis de Man. 

 Synalpheus amboince (Zehntner). 

 Synalpheus consobrinus de Man. 

 Synalpheus odontophorus de Man. 



* Synalpheus brucei Potts. 

 Synalpheus albatrossi Coutiere. 



