86 DR. C. L. BOULENGER ON 



1 905 and were sent, together with the other Annelida, to Mr. F. 

 Potts, of Trinity Hall, Cambridge, who submitted them to me for 

 examination. 



Mr. Crossland's collection is of considerable interest, since very- 

 little is known of the Red Sea Myzostomida, and the only two 

 species recorded from that locality were described from very scanty 

 material. 



The material as I received it from Mr. Potts consisted of six 

 tubes containing about 1 70 specimens. Of these six belong to a 

 species hithei-to unknown and which I take great pleasure in 

 dedicating to Mr. Crossland ; two I have referred to v. Graff's 

 Myzostoma rubrofasciatum, described from a single specimen in 

 1884; whilst the remainder belong to a species which I take to 

 be the old-established form Myzostoma costatimi, one of the first 

 three species of the group described by Leuckart so long ago as 

 1830. 



The importance of a collection of this kind, however, is not to 

 be judged by the number of species repi-esented in it. About 

 100 species of Myzostoma are on record and of these by far the 

 greater number have been described from external characters 

 only, ill-preserved or limited material having made a complete 

 examination impossible. Mr. Crossland's specimens were in an 

 excellent state of preservation and I have been able to give a 

 fairly complete account of the anatomy of two of the forms men- 

 tioned above ; moreover, the very large series of specimens of 

 M. costatum reveals a range of variation remarkable even for this 

 group of animals, and affords an opportunity of judging the 

 mei'its of various characters for S)^stematic purposes. 



In my descriptions of the species I have endeavoured to give as 

 complete an account as possible of the general morphology of the 

 various organs, especially of those which might be of taxonomic 

 interest. I have, however, refrained from attempting any histo- 

 logical decriptions, as I felt it useless to do so without material 

 specially preserved for such a purpose. Throughout this paper I 

 have retained as far as possible the nomenclature of parts used 

 by V. Graff (7-9) * and Hansen (15), and have not followed the 

 example set by some of the more recent workers on the 

 Myzostomida. 



I desire to take this opportunity of thanking Mi-. Potts for en- 

 trusting me with this valuable material ; Prof. F. Jeffrey Bell 

 very kindly allowed me to examine some of the types of the 

 ' Challenger ' collection of Myzostomida preserved in the British 

 Museum (Natural History), and I am also indebted to Mr. H. C. 

 Chadwick, of the Port Erin Biological Station, for information 

 concerning the Red Sea Echinoderms from which Mr. Crossland's 

 specimens were obtained f. 



* The figures in brackets refer to the List of References on p. 107. 

 t I also wish to express my indebtedness to Mr. Cox, of the Zoological Depart- 

 ment of this University, for the excellent photographs reproduced on PI. VIII. 



