252 ^'/ie Philippine Journal of Science i9is 



Spengel has studied the dermal muscle layer of all of these 

 forms, and on the basis of the difference in this structure he has 

 divided the genus Thalassema into three separate groups, with- 

 out regard to the number of longitudinal muscle bundles which 

 they display. In the forms which have been described as having 

 separate bundles of longitudinal muscle, he finds that "all have 

 an uninterrupted, continuous layer of longitudinal muscle which 

 is regularly thickened and intermittently thinned," thus giving 

 the appearance of separate bundles except when examined very 

 carefully under the microscope. He says also that in all forms 

 the circular or ring muscle forms a continuous uniform sheet. 

 Therefore, he separates his groups according to the degree in 

 which this thickening and thinning of the longitudinal layer is 

 found and the manner in which it occurs. 



The first group for which he retains the generic name Thalas- 

 sema and for which he takes the type species, T. neptunii 

 Gaertner, as the type, has the following characteristics. The 

 longitudinal muscle is of uniform thickness throughout, and the 

 oblique muscle is also of uniform thickness and completely covers 

 the longitudinal layer. The second group to which he gives the 

 generic name Listnolobus is characterized as follows: The lon- 

 gitudinal muscle is thickened into bundles at intervals, and is 

 not interrupted between the bundles, but simply becomes 

 thinner, forming undulations. The oblique layer is like that 

 of Thalassema; that is, of uniform thickness and completely 

 covering the longitudinal layer. To this genus he assigns 

 T. erythrogrammon of Sluiter and Wilson and the specimen 

 which he has from Florida. To the third group he gives the old 

 generic name of Riippell — Ochetostoma. This group is charac- 

 terized by having the main part of the longitudinal muscle in- 

 terrupted by "intervals," so that longitudinal bundles are formed 

 which appear to be separated, but are in reality connected by a 

 very thin layer of longitudinal fibers between the bundles. The 

 oblique muscle does not follow the longitudinal layer in the inter- 

 vals, but bridges the intervals on septal bands of connective 

 tissue. Also, the oblique muscle is not a continuous sheet as in 

 the other forms, but is separated into bundles over the "inter- 

 vals," so that these are connected with the ccelom by openings 

 between these oblique bundles. In this genus he places the orig- 

 inal T. erythrogrammon of Riippell and Lambert's T. caudex. 

 The position of the other specimens he does not define. 



The dermal muscle layer of T. griffini bears a very close 

 resemblance to that of T. erythrogrammon Riippell, but there 

 are some differences from the condition which Spengel describes 



