THE MARINE TURBELLARIA. 305 



genus Thysanozoon , and consequently Thysanoplana must be referred to the synonymy of that 

 genus. When it becomes advantageous to divide up the genus, the best guide to a correct 

 grouping of the species will probably be found in the presence or absence of gut-diverticula 

 in the dorsal papillae. 



Distribution in the Indian Ocean. Great interest attaches to Mr Stanley Gardiner's 

 collection owing to the fact that it is not only the first made in the neighbourhood of the 

 Maldive and Laccadive Archipelagoes, but also that it is one of the largest ever made in the 

 Indian Ocean ; certainly the largest since the publication of Lang's Monograph. It is not of 

 course possible on our present knowledge of exotic forms to discuss the distribution of marine 

 Turbellaria, yet a few points are worthy of remark in connection with these specimens. 



Firstly, it will be noted that the Euryleptidae are entirely lacking in the collection. We 

 must not assume therefore that they are altogether absent from the reefs of the Archipelago, 

 but we are certainly justified in supposing them to be of considerable rarity in that neigh- 

 bourhood. This is the more remarkable when we remember that the Euryleptidae are well 

 represented on the coast of Ceylon, and are known to occur in most seas. 



I quote here an extract from Mr Gardiner's notes : " I have no lists, nor can I find any 

 account of the Turbellaria round continental tropical coasts, on which to base any comparisons 

 as to the relative abundance of the group in the Maldives. From a limited examination of 

 some reefs at Weligama and off the Jaffna coast of Ceylon I am inclined to think that they 

 are very much less abundant in the Maldives, both in number and variety of species." 



Secondly, the relatively high percentage of Pseudoceridae in the collection is striking. In 

 addition to the five or six species of Pseudoceros given in the systematic part there are frag- 

 ments of a specimen, which must I believe be referred to this genus, but is too much broken 

 to describe. 



Probably the Prosthiostomidae and Cestoplanidae will prove to be abundant over the 

 whole of the Indian Ocean, and we may expect to find, especially in the latter family, forms 

 of great interest. I have in my possession a collection of Turbellaria made by Mr Evans 

 near Penang. This collection contains not less than two new Cestoplanoids, one of them 

 a very remarkable creature with a complete series of marginal eyes which are much more 

 numerous than those of Cestoplana maldivensis; its body also is relatively much longer. 



Lastly, the occurrence of Pericelis byerleyana and of Leptoplana pardalis in the Tropical 

 Pacific as well as in the Maldives' Archipelago is of interest. Two other widely distributed 

 species, Leptoplana tremellaris and Thysanozoon brocchii, are known, but both of these occur in 

 north temperate as well as in tropical seas. 



Parasites. In none of the specimens in this collection, of which I have cut serial 

 sections, have I found any gregarine parasite such as that which is found commonly in 

 Leptoplana tremellaris^. On the other hand I would call special attention to the occurrence 

 in two species, viz. Planocera armata and Prosthiostomum elegans, of bacteria or bacteria-like 

 structures, which in both cases, but especially in the former, appear to occur only in certain 

 definite situations. 



GuT-DlVERTlCULA. Similar gut-diverticula to those found in Planocera armata occur also 

 in other Planoceroids. Whilst moi-phologically they are not unlike the diverticula which invade 



' I have not been able to identify this species. Discocelis tigrinia is infested with Ophiodina discocelidk Mengazzini, 

 which is probably closely allied to it. 



39—2 



