REPORT ON THE TUNICATA. 51 



Suborder II. HEMIMYAEIA. 



Free-swimmiug pelagic forms which exhibit alternation of generations in their life- 

 history and in the sexual condition form temporary colonies. 



The body is more or less fusiform, with the longer axis antero-posterior, and the 

 branchial and atrial apertures nearly terminal. 



The test is well developed. 



The musculature of the mantle is in the form of a series of transversely running 

 bands, which do not form complete and independent rings as in the Cyclomyaria. 



The branchial and peribranchial cavities form a continuous space in the interior of 

 the body opening exteruallj^ by the branchial and atrial apertures, and traversed 

 obliquely from the dorsal and anterior end to the ventral and posterior by a long 

 narrow vascular band, which represents the dorsal lamina, the dorsal blood-vessel, 

 and the neighbouring part of the dorsal edge of the branchial sac of an ordinary 

 Ascidian. 



The alimentary canal is placed ventrally. It may be either stretched out, so as to 

 extend for some distance anteriorly, or, as is more usual, be concentrated to form along 

 with the reproductive organs a rounded opaque mass near the posterior end of the body, 

 known as the visceral mass or " nucleus." 



The embryonic development is direct, no tailed larva being formed. 



I have formed this suborder to correspond with Uljanin's group Cyclomyaria. The 

 name Hemimyaria refers to the incomplete condition of the muscular rings. The 

 suborder includes two very distinct families, the SalpidtE, which contains the typical 

 members of the group, and the Octacnemid^, including a single very remarkable form 

 [Octacnemus bythius, ]\Ioseley), which in some respects does not conform with the 

 characters given above.' 



o* 



Family I. Salpidje. 



Body not attached, elongated ; branchial and atrial apertures at the opposite ends. 



Test well developed, gelatinous or cartilaginous. 



Mantle with well-marked muscle bands, which, however, do not form complete rings, 

 but are wanting ventrally. 



Brayichial and Peribranchial Cavities forming a large central space opening to the 

 exterior at both ends ; side walls of branchial sac not developed. 



Dorsal Lamina in the form of a vascular band traversing the central cavity. 



'Alimentary Canal usually forming a small coiled mass placed posteriorly and 

 ventrally. 



1 See below, p. 88. 



